diff --git a/composer.json b/composer.json
index 9babd7a..3550492 100644
--- a/composer.json
+++ b/composer.json
@@ -10,7 +10,7 @@
         "webmozart/assert": "^1.2"
     },
     "require-dev": {
-        "phpunit/phpunit": "~4.8",
+        "phpunit/phpunit": "^7.5",
         "php-http/guzzle6-adapter": "^1.0",
         "nyholm/psr7": "^1.0",
         "nyholm/nsa": "^1.1"
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index f8802a3..1000dd2 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -3,11 +3,9 @@
          colors="true"
          processIsolation="false"
          stopOnFailure="false"
-         syntaxCheck="false"
          convertErrorsToExceptions="true"
          convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
-         testSuiteLoaderClass="PHPUnit_Runner_StandardTestSuiteLoader">
+         convertWarningsToExceptions="true">
 
     <testsuites>
         <testsuite name="Mailgun test suite">
diff --git a/src/Api/Attachment.php b/src/Api/Attachment.php
index 008aef9..0e1a171 100644
--- a/src/Api/Attachment.php
+++ b/src/Api/Attachment.php
@@ -11,6 +11,7 @@ namespace Mailgun\Api;
 
 use Mailgun\Assert;
 use Mailgun\Model\Attachment\Attachment as Model;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
@@ -18,11 +19,9 @@ use Mailgun\Model\Attachment\Attachment as Model;
 class Attachment extends HttpApi
 {
     /**
-     * @param string $url
-     *
-     * @return Model
+     * @return Model|ResponseInterface
      */
-    public function show($url)
+    public function show(string $url)
     {
         Assert::stringNotEmpty($url);
         Assert::regex($url, '@https://.*mailgun\.(net|org)/v.+@');
diff --git a/src/Api/Domain.php b/src/Api/Domain.php
index d67f96d..d6431b9 100644
--- a/src/Api/Domain.php
+++ b/src/Api/Domain.php
@@ -38,11 +38,8 @@ class Domain extends HttpApi
      *
      * @return IndexResponse
      */
-    public function index($limit = 100, $skip = 0)
+    public function index(int $limit = 100, int $skip = 0)
     {
-        Assert::integer($limit);
-        Assert::integer($skip);
-
         $params = [
             'limit' => $limit,
             'skip' => $skip,
@@ -60,7 +57,7 @@ class Domain extends HttpApi
      *
      * @return ShowResponse|array|ResponseInterface
      */
-    public function show($domain)
+    public function show(string $domain)
     {
         Assert::stringNotEmpty($domain);
 
@@ -83,7 +80,7 @@ class Domain extends HttpApi
      *
      * @return CreateResponse|array|ResponseInterface
      */
-    public function create($domain, $smtpPass = null, $spamAction = null, $wildcard = null)
+    public function create(string $domain, string $smtpPass = null, string $spamAction = null, bool $wildcard = null)
     {
         Assert::stringNotEmpty($domain);
 
@@ -112,7 +109,7 @@ class Domain extends HttpApi
      *
      * @return DeleteResponse|array|ResponseInterface
      */
-    public function delete($domain)
+    public function delete(string $domain)
     {
         Assert::stringNotEmpty($domain);
 
@@ -130,12 +127,9 @@ class Domain extends HttpApi
      *
      * @return CredentialResponse
      */
-    public function credentials($domain, $limit = 100, $skip = 0)
+    public function credentials(string $domain, int $limit = 100, int $skip = 0)
     {
         Assert::stringNotEmpty($domain);
-        Assert::integer($limit);
-        Assert::integer($skip);
-
         $params = [
             'limit' => $limit,
             'skip' => $skip,
@@ -155,7 +149,7 @@ class Domain extends HttpApi
      *
      * @return CreateCredentialResponse|array|ResponseInterface
      */
-    public function createCredential($domain, $login, $password)
+    public function createCredential(string $domain, string $login, string $password)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($login);
@@ -181,7 +175,7 @@ class Domain extends HttpApi
      *
      * @return UpdateCredentialResponse|array|ResponseInterface
      */
-    public function updateCredential($domain, $login, $pass)
+    public function updateCredential(string $domain, string $login, string $pass)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($login);
@@ -205,7 +199,7 @@ class Domain extends HttpApi
      *
      * @return DeleteCredentialResponse|array|ResponseInterface
      */
-    public function deleteCredential($domain, $login)
+    public function deleteCredential(string $domain, string $login)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($login);
@@ -228,7 +222,7 @@ class Domain extends HttpApi
      *
      * @return ConnectionResponse|ResponseInterface
      */
-    public function connection($domain)
+    public function connection(string $domain)
     {
         Assert::stringNotEmpty($domain);
 
@@ -247,12 +241,9 @@ class Domain extends HttpApi
      *
      * @return UpdateConnectionResponse|array|ResponseInterface
      */
-    public function updateConnection($domain, $requireTLS, $noVerify)
+    public function updateConnection(string $domain, ?bool $requireTLS, ?bool $noVerify)
     {
         Assert::stringNotEmpty($domain);
-        Assert::nullOrBoolean($requireTLS);
-        Assert::nullOrBoolean($noVerify);
-
         $params = [];
 
         if (null !== $requireTLS) {
@@ -275,7 +266,7 @@ class Domain extends HttpApi
      *
      * @return VerifyResponse|array|ResponseInterface
      */
-    public function verify($domain)
+    public function verify(string $domain)
     {
         Assert::stringNotEmpty($domain);
 
diff --git a/src/Api/Event.php b/src/Api/Event.php
index a44cf71..e9f1b4e 100644
--- a/src/Api/Event.php
+++ b/src/Api/Event.php
@@ -27,7 +27,7 @@ class Event extends HttpApi
      *
      * @return EventResponse
      */
-    public function get($domain, array $params = [])
+    public function get(string $domain, array $params = [])
     {
         Assert::stringNotEmpty($domain);
 
diff --git a/src/Api/HttpApi.php b/src/Api/HttpApi.php
index 08ef0bf..70ab2c9 100644
--- a/src/Api/HttpApi.php
+++ b/src/Api/HttpApi.php
@@ -16,7 +16,7 @@ use Mailgun\Hydrator\Hydrator;
 use Mailgun\Hydrator\NoopHydrator;
 use Mailgun\Exception\HttpClientException;
 use Mailgun\Exception\HttpServerException;
-use Mailgun\RequestBuilder;
+use Mailgun\HttpClient\RequestBuilder;
 use Psr\Http\Message\ResponseInterface;
 
 /**
@@ -41,11 +41,6 @@ abstract class HttpApi
      */
     protected $requestBuilder;
 
-    /**
-     * @param HttpClient     $httpClient
-     * @param RequestBuilder $requestBuilder
-     * @param Hydrator       $hydrator
-     */
     public function __construct(HttpClient $httpClient, RequestBuilder $requestBuilder, Hydrator $hydrator)
     {
         $this->httpClient = $httpClient;
@@ -63,7 +58,7 @@ abstract class HttpApi
      *
      * @throws \Exception
      */
-    protected function hydrateResponse(ResponseInterface $response, $class)
+    protected function hydrateResponse(ResponseInterface $response, string $class)
     {
         if (!$this->hydrator) {
             return $response;
@@ -79,8 +74,6 @@ abstract class HttpApi
     /**
      * Throw the correct exception for this error.
      *
-     * @param ResponseInterface $response
-     *
      * @throws \Exception
      */
     protected function handleErrors(ResponseInterface $response)
@@ -110,10 +103,8 @@ abstract class HttpApi
      * @param string $path           Request path
      * @param array  $parameters     GET parameters
      * @param array  $requestHeaders Request Headers
-     *
-     * @return ResponseInterface
      */
-    protected function httpGet($path, array $parameters = [], array $requestHeaders = [])
+    protected function httpGet(string $path, array $parameters = [], array $requestHeaders = []): ResponseInterface
     {
         if (count($parameters) > 0) {
             $path .= '?'.http_build_query($parameters);
@@ -136,10 +127,8 @@ abstract class HttpApi
      * @param string $path           Request path
      * @param array  $parameters     POST parameters
      * @param array  $requestHeaders Request headers
-     *
-     * @return ResponseInterface
      */
-    protected function httpPost($path, array $parameters = [], array $requestHeaders = [])
+    protected function httpPost(string $path, array $parameters = [], array $requestHeaders = []): ResponseInterface
     {
         return $this->httpPostRaw($path, $this->createRequestBody($parameters), $requestHeaders);
     }
@@ -150,10 +139,8 @@ abstract class HttpApi
      * @param string       $path           Request path
      * @param array|string $body           Request body
      * @param array        $requestHeaders Request headers
-     *
-     * @return ResponseInterface
      */
-    protected function httpPostRaw($path, $body, array $requestHeaders = [])
+    protected function httpPostRaw(string $path, $body, array $requestHeaders = []): ResponseInterface
     {
         try {
             $response = $this->httpClient->sendRequest(
@@ -172,10 +159,8 @@ abstract class HttpApi
      * @param string $path           Request path
      * @param array  $parameters     PUT parameters
      * @param array  $requestHeaders Request headers
-     *
-     * @return ResponseInterface
      */
-    protected function httpPut($path, array $parameters = [], array $requestHeaders = [])
+    protected function httpPut(string $path, array $parameters = [], array $requestHeaders = []): ResponseInterface
     {
         try {
             $response = $this->httpClient->sendRequest(
@@ -194,10 +179,8 @@ abstract class HttpApi
      * @param string $path           Request path
      * @param array  $parameters     DELETE parameters
      * @param array  $requestHeaders Request headers
-     *
-     * @return ResponseInterface
      */
-    protected function httpDelete($path, array $parameters = [], array $requestHeaders = [])
+    protected function httpDelete(string $path, array $parameters = [], array $requestHeaders = []): ResponseInterface
     {
         try {
             $response = $this->httpClient->sendRequest(
@@ -217,7 +200,7 @@ abstract class HttpApi
      *
      * @return array
      */
-    protected function createRequestBody(array $parameters)
+    private function createRequestBody(array $parameters): array
     {
         $resources = [];
         foreach ($parameters as $key => $values) {
diff --git a/src/Api/Ip.php b/src/Api/Ip.php
index c69f5ca..3e4daee 100644
--- a/src/Api/Ip.php
+++ b/src/Api/Ip.php
@@ -25,11 +25,10 @@ class Ip extends HttpApi
     /**
      * Returns a list of IPs.
      *
-     * @param bool $dedicated
      *
      * @return IndexResponse|ResponseInterface
      */
-    public function index($dedicated = false)
+    public function index(bool $dedicated = false)
     {
         Assert::boolean($dedicated);
 
@@ -45,11 +44,10 @@ class Ip extends HttpApi
     /**
      * Returns a list of IPs assigned to a domain.
      *
-     * @param string $domain
      *
      * @return IndexResponse|ResponseInterface
      */
-    public function domainIndex($domain)
+    public function domainIndex(string $domain)
     {
         Assert::stringNotEmpty($domain);
 
@@ -61,11 +59,10 @@ class Ip extends HttpApi
     /**
      * Returns a single ip.
      *
-     * @param string $ip
      *
      * @return ShowResponse|ResponseInterface
      */
-    public function show($ip)
+    public function show(string $ip)
     {
         Assert::ip($ip);
 
@@ -77,12 +74,10 @@ class Ip extends HttpApi
     /**
      * Assign a dedicated IP to the domain specified.
      *
-     * @param string $domain
-     * @param string $ip
      *
      * @return UpdateResponse|ResponseInterface
      */
-    public function assign($domain, $ip)
+    public function assign(string $domain, string $ip)
     {
         Assert::stringNotEmpty($domain);
         Assert::ip($ip);
@@ -99,12 +94,11 @@ class Ip extends HttpApi
     /**
      * Unassign an IP from the domain specified.
      *
-     * @param string $domain
-     * @param string $ip
+
      *
      * @return UpdateResponse|ResponseInterface
      */
-    public function unassign($domain, $ip)
+    public function unassign(string $domain, string $ip)
     {
         Assert::stringNotEmpty($domain);
         Assert::ip($ip);
diff --git a/src/Api/MailingList.php b/src/Api/MailingList.php
index 7091657..40e422e 100644
--- a/src/Api/MailingList.php
+++ b/src/Api/MailingList.php
@@ -19,10 +19,7 @@ use Mailgun\Model\MailingList\UpdateResponse;
 
 class MailingList extends HttpApi
 {
-    /**
-     * @return Member
-     */
-    public function member()
+    public function member(): Member
     {
         return new Member($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
@@ -36,7 +33,7 @@ class MailingList extends HttpApi
      *
      * @throws \Exception
      */
-    public function pages($limit = 100)
+    public function pages(int $limit = 100)
     {
         Assert::integer($limit);
         Assert::greaterThan($limit, 0);
@@ -62,7 +59,7 @@ class MailingList extends HttpApi
      *
      * @throws \Exception
      */
-    public function create($address, $name = null, $description = null, $accessLevel = 'readonly')
+    public function create(string $address, string $name = null, string $description = null, string $accessLevel = 'readonly')
     {
         Assert::stringNotEmpty($address);
         Assert::nullOrStringNotEmpty($name);
@@ -90,7 +87,7 @@ class MailingList extends HttpApi
      *
      * @throws \Exception
      */
-    public function show($address)
+    public function show(string $address)
     {
         Assert::stringNotEmpty($address);
 
@@ -109,7 +106,7 @@ class MailingList extends HttpApi
      *
      * @throws \Exception
      */
-    public function update($address, $parameters = [])
+    public function update(string $address, array $parameters = [])
     {
         Assert::stringNotEmpty($address);
         Assert::isArray($parameters);
@@ -143,7 +140,7 @@ class MailingList extends HttpApi
      *
      * @throws \Exception
      */
-    public function delete($address)
+    public function delete(string $address)
     {
         Assert::stringNotEmpty($address);
 
diff --git a/src/Api/MailingList/Member.php b/src/Api/MailingList/Member.php
index 3fe2fd5..02fc938 100644
--- a/src/Api/MailingList/Member.php
+++ b/src/Api/MailingList/Member.php
@@ -26,24 +26,27 @@ class Member extends HttpApi
      *
      * @param string      $address    Address of the mailing list
      * @param int         $limit      Maximum number of records to return (optional: 100 by default)
-     * @param string|null $subscribed `yes` to lists subscribed, `no` for unsubscribed. list all if null
+     * @param string|null $subscribed `true` to lists subscribed, `false` for unsubscribed. list all if null
      *
      * @return IndexResponse
      *
      * @throws \Exception
      */
-    public function index($address, $limit = 100, $subscribed = null)
+    public function index(string $address, int $limit = 100, bool $subscribed = null)
     {
         Assert::stringNotEmpty($address);
-        Assert::integer($limit);
         Assert::greaterThan($limit, 0);
-        Assert::oneOf($subscribed, [null, 'yes', 'no']);
 
         $params = [
             'limit' => $limit,
-            'subscribed' => $subscribed,
         ];
 
+        if (true === $subscribed) {
+            $params['subscribed'] = 'yes';
+        } elseif (false === $subscribed) {
+            $params['subscribed'] = 'no';
+        }
+
         $response = $this->httpGet(sprintf('/v3/lists/%s/members/pages', $address), $params);
 
         return $this->hydrateResponse($response, IndexResponse::class);
@@ -59,7 +62,7 @@ class Member extends HttpApi
      *
      * @throws \Exception
      */
-    public function show($list, $address)
+    public function show(string $list, string $address)
     {
         Assert::stringNotEmpty($list);
         Assert::stringNotEmpty($address);
@@ -76,27 +79,25 @@ class Member extends HttpApi
      * @param string $address    Address for the member
      * @param string $name       Name for the member (optional)
      * @param array  $vars       Array of field => value pairs to store additional data
-     * @param string $subscribed `yes` to add as subscribed (default), `no` as unsubscribed
-     * @param string $upsert     `yes` to update member if present, `no` to raise error in case of a duplicate member (default)
+     * @param bool   $subscribed `true` to add as subscribed (default), `false` as unsubscribed
+     * @param bool   $upsert     `true` to update member if present, `false` to raise error in case of a duplicate member (default)
      *
      * @return CreateResponse
      *
      * @throws \Exception
      */
-    public function create($list, $address, $name = null, array $vars = [], $subscribed = 'yes', $upsert = 'no')
+    public function create(string $list, string $address, string $name = null, array $vars = [], bool $subscribed = true, bool $upsert = false)
     {
         Assert::stringNotEmpty($list);
         Assert::stringNotEmpty($address);
         Assert::nullOrStringNotEmpty($name);
-        Assert::oneOf($subscribed, ['yes', 'no']);
-        Assert::oneOf($upsert, ['yes', 'no']);
 
         $params = [
             'address' => $address,
             'name' => $name,
             'vars' => $vars,
-            'subscribed' => $subscribed,
-            'upsert' => $upsert,
+            'subscribed' => $subscribed ? 'yes' : 'no',
+            'upsert' => $upsert ? 'yes' : 'no',
         ];
 
         $response = $this->httpPost(sprintf('/v3/lists/%s/members', $list), $params);
@@ -109,13 +110,13 @@ class Member extends HttpApi
      *
      * @param string $list    Address of the mailing list
      * @param array  $members Array of members, each item should be either a single string address or an array of member properties
-     * @param string $upsert  `yes` to update existing members, `no` (default) to ignore duplicates
+     * @param string $upsert  `true` to update existing members, `false` (default) to ignore duplicates
      *
      * @return UpdateResponse
      *
      * @throws \Exception
      */
-    public function createMultiple($list, array $members, $upsert = 'no')
+    public function createMultiple(string $list, array $members, $upsert = false)
     {
         Assert::stringNotEmpty($list);
         Assert::isArray($members);
@@ -129,8 +130,6 @@ class Member extends HttpApi
             ));
         }
 
-        Assert::oneOf($upsert, ['yes', 'no']);
-
         foreach ($members as $data) {
             if (is_string($data)) {
                 Assert::stringNotEmpty($data);
@@ -164,7 +163,7 @@ class Member extends HttpApi
 
         $params = [
             'members' => json_encode($members),
-            'upsert' => $upsert,
+            'upsert' => $upsert ? 'yes' : 'no',
         ];
 
         $response = $this->httpPost(sprintf('/v3/lists/%s/members.json', $list), $params);
@@ -183,7 +182,7 @@ class Member extends HttpApi
      *
      * @throws \Exception
      */
-    public function update($list, $address, $parameters = [])
+    public function update(string $list, string $address, array $parameters = [])
     {
         Assert::stringNotEmpty($list);
         Assert::stringNotEmpty($address);
@@ -222,7 +221,7 @@ class Member extends HttpApi
      *
      * @throws \Exception
      */
-    public function delete($list, $address)
+    public function delete(string $list, string $address)
     {
         Assert::stringNotEmpty($list);
         Assert::stringNotEmpty($address);
diff --git a/src/Api/Message.php b/src/Api/Message.php
index 201ecb7..92c6423 100644
--- a/src/Api/Message.php
+++ b/src/Api/Message.php
@@ -14,30 +14,22 @@ use Mailgun\Exception\InvalidArgumentException;
 use Mailgun\Message\BatchMessage;
 use Mailgun\Model\Message\SendResponse;
 use Mailgun\Model\Message\ShowResponse;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  */
 class Message extends HttpApi
 {
-    /**
-     * @param string $domain
-     * @param bool   $autoSend
-     *
-     * @return BatchMessage
-     */
-    public function getBatchMessage($domain, $autoSend = true)
+    public function getBatchMessage(string $domain, bool $autoSend = true): BatchMessage
     {
         return new BatchMessage($this, $domain, $autoSend);
     }
 
     /**
-     * @param string $domain
-     * @param array  $params
-     *
-     * @return SendResponse
+     * @return SendResponse|ResponseInterface
      */
-    public function send($domain, array $params)
+    public function send(string $domain, array $params)
     {
         Assert::string($domain);
         Assert::notEmpty($domain);
@@ -70,8 +62,10 @@ class Message extends HttpApi
      * @param array  $recipients with all you send emails to. Including bcc and cc
      * @param string $message    Message filepath or content
      * @param array  $params
+     *
+     * @return SendResponse|ResponseInterface
      */
-    public function sendMime($domain, array $recipients, $message, array $params)
+    public function sendMime(string $domain, array $recipients, string  $message, array $params)
     {
         Assert::string($domain);
         Assert::notEmpty($domain);
@@ -103,9 +97,9 @@ class Message extends HttpApi
      * @param string $url
      * @param bool   $rawMessage if true we will use "Accept: message/rfc2822" header
      *
-     * @return ShowResponse
+     * @return ShowResponse|ResponseInterface
      */
-    public function show($url, $rawMessage = false)
+    public function show(string $url, bool $rawMessage = false)
     {
         Assert::notEmpty($url);
 
@@ -120,16 +114,11 @@ class Message extends HttpApi
     }
 
     /**
-     * Prepare a file.
-     *
-     * @param string $fieldName
-     * @param array  $filePath  array('fileContent' => 'content') or array('filePath' => '/foo/bar')
-     *
-     * @return array
+     * @param array $filePath array('fileContent' => 'content') or array('filePath' => '/foo/bar')
      *
      * @throws InvalidArgumentException
      */
-    private function prepareFile($fieldName, array $filePath)
+    private function prepareFile(string $fieldName, array $filePath): array
     {
         $filename = isset($filePath['filename']) ? $filePath['filename'] : null;
 
@@ -161,12 +150,8 @@ class Message extends HttpApi
 
     /**
      * Prepare multipart parameters. Make sure each POST parameter is split into an array with 'name' and 'content' keys.
-     *
-     * @param array $params
-     *
-     * @return array
      */
-    private function prepareMultipartParameters(array $params)
+    private function prepareMultipartParameters(array $params): array
     {
         $postDataMultipart = [];
         foreach ($params as $key => $value) {
@@ -184,10 +169,8 @@ class Message extends HttpApi
 
     /**
      * Close open resources.
-     *
-     * @param array $params
      */
-    private function closeResources(array $params)
+    private function closeResources(array $params): void
     {
         foreach ($params as $param) {
             if (is_array($param) && array_key_exists('content', $param) && is_resource($param['content'])) {
diff --git a/src/Api/Pagination.php b/src/Api/Pagination.php
index 4288d41..279dc96 100644
--- a/src/Api/Pagination.php
+++ b/src/Api/Pagination.php
@@ -18,62 +18,36 @@ use Psr\Http\Message\ResponseInterface;
  */
 trait Pagination
 {
-    abstract protected function httpGet($path, array $parameters = [], array $requestHeaders = []);
+    abstract protected function httpGet(string $path, array $parameters = [], array $requestHeaders = []): ResponseInterface;
 
-    abstract protected function hydrateResponse(ResponseInterface $response, $className);
+    abstract protected function hydrateResponse(ResponseInterface $response, string $className);
 
-    /**
-     * @param PagingProvider $response
-     *
-     * @return PagingProvider|null
-     */
-    public function nextPage(PagingProvider $response)
+    public function nextPage(PagingProvider $response): ?PagingProvider
     {
         return $this->getPaginationUrl($response->getNextUrl(), get_class($response));
     }
 
-    /**
-     * @param PagingProvider $response
-     *
-     * @return PagingProvider|null
-     */
-    public function previousPage(PagingProvider $response)
+    public function previousPage(PagingProvider $response): ?PagingProvider
     {
         return $this->getPaginationUrl($response->getPreviousUrl(), get_class($response));
     }
 
-    /**
-     * @param PagingProvider $response
-     *
-     * @return PagingProvider|null
-     */
-    public function firstPage(PagingProvider $response)
+    public function firstPage(PagingProvider $response): ?PagingProvider
     {
         return $this->getPaginationUrl($response->getFirstUrl(), get_class($response));
     }
 
-    /**
-     * @param PagingProvider $response
-     *
-     * @return PagingProvider|null
-     */
-    public function lastPage(PagingProvider $response)
+    public function lastPage(PagingProvider $response): ?PagingProvider
     {
         return $this->getPaginationUrl($response->getLastUrl(), get_class($response));
     }
 
-    /**
-     * @param string $url
-     * @param string $class
-     *
-     * @return PagingProvider|null
-     */
-    private function getPaginationUrl($url, $class)
+    private function getPaginationUrl(string $url, string $class): ?PagingProvider
     {
         Assert::stringNotEmpty($class);
 
         if (empty($url)) {
-            return;
+            return null;
         }
 
         $response = $this->httpGet($url);
diff --git a/src/Api/Route.php b/src/Api/Route.php
index c6d980d..87d5b62 100644
--- a/src/Api/Route.php
+++ b/src/Api/Route.php
@@ -31,10 +31,8 @@ class Route extends HttpApi
      *
      * @return IndexResponse
      */
-    public function index($limit = 100, $skip = 0)
+    public function index(int $limit = 100, int $skip = 0)
     {
-        Assert::integer($limit);
-        Assert::integer($skip);
         Assert::greaterThan($limit, 0);
         Assert::greaterThanEq($skip, 0);
 
@@ -55,7 +53,7 @@ class Route extends HttpApi
      *
      * @return ShowResponse
      */
-    public function show($routeId)
+    public function show(string $routeId)
     {
         Assert::stringNotEmpty($routeId);
 
@@ -74,12 +72,9 @@ class Route extends HttpApi
      *
      * @return CreateResponse
      */
-    public function create($expression, array $actions, $description, $priority = 0)
+    public function create(string $expression, array $actions, string $description, int $priority = 0)
     {
-        Assert::string($expression);
         Assert::isArray($actions);
-        Assert::string($description);
-        Assert::integer($priority);
 
         $params = [
             'priority' => $priority,
@@ -105,14 +100,14 @@ class Route extends HttpApi
      *
      * @return UpdateResponse
      */
-    public function update($routeId, $expression = null, array $actions = [], $description = null, $priority = null)
-    {
+    public function update(
+        string $routeId,
+        string $expression = null,
+        array $actions = [],
+        string $description = null,
+        int $priority = null
+    ) {
         Assert::stringNotEmpty($routeId);
-        Assert::nullOrString($expression);
-        Assert::isArray($actions);
-        Assert::nullOrString($description);
-        Assert::nullOrInteger($priority);
-
         $params = [];
 
         if (!empty($expression)) {
@@ -146,7 +141,7 @@ class Route extends HttpApi
      *
      * @return DeleteResponse
      */
-    public function delete($routeId)
+    public function delete(string $routeId)
     {
         Assert::stringNotEmpty($routeId);
 
diff --git a/src/Api/Stats.php b/src/Api/Stats.php
index d6f9fd3..d288fca 100644
--- a/src/Api/Stats.php
+++ b/src/Api/Stats.php
@@ -21,12 +21,9 @@ use Mailgun\Model\Stats\TotalResponse;
 class Stats extends HttpApi
 {
     /**
-     * @param string $domain
-     * @param array  $params
-     *
      * @return TotalResponse|array
      */
-    public function total($domain, array $params = [])
+    public function total(string $domain, array $params = [])
     {
         Assert::stringNotEmpty($domain);
 
@@ -36,12 +33,9 @@ class Stats extends HttpApi
     }
 
     /**
-     * @param $domain
-     * @param array $params
-     *
      * @return AllResponse|array
      */
-    public function all($domain, array $params = [])
+    public function all(string $domain, array $params = [])
     {
         Assert::stringNotEmpty($domain);
 
diff --git a/src/Api/Suppression.php b/src/Api/Suppression.php
index 8312116..14b46d7 100644
--- a/src/Api/Suppression.php
+++ b/src/Api/Suppression.php
@@ -14,7 +14,7 @@ use Mailgun\Api\Suppression\Bounce;
 use Mailgun\Api\Suppression\Complaint;
 use Mailgun\Api\Suppression\Unsubscribe;
 use Mailgun\Hydrator\Hydrator;
-use Mailgun\RequestBuilder;
+use Mailgun\HttpClient\RequestBuilder;
 
 /**
  * @see https://documentation.mailgun.com/api-suppressions.html
@@ -38,11 +38,6 @@ class Suppression
      */
     private $hydrator;
 
-    /**
-     * @param HttpClient     $httpClient
-     * @param RequestBuilder $requestBuilder
-     * @param Hydrator       $hydrator
-     */
     public function __construct(HttpClient $httpClient, RequestBuilder $requestBuilder, Hydrator $hydrator)
     {
         $this->httpClient = $httpClient;
@@ -50,26 +45,17 @@ class Suppression
         $this->hydrator = $hydrator;
     }
 
-    /**
-     * @return Bounce
-     */
-    public function bounces()
+    public function bounces(): Bounce
     {
         return new Bounce($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Complaint
-     */
-    public function complaints()
+    public function complaints(): Complaint
     {
         return new Complaint($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Unsubscribe
-     */
-    public function unsubscribes()
+    public function unsubscribes(): Unsubscribe
     {
         return new Unsubscribe($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
diff --git a/src/Api/Suppression/Bounce.php b/src/Api/Suppression/Bounce.php
index 1f66aca..8a6e920 100644
--- a/src/Api/Suppression/Bounce.php
+++ b/src/Api/Suppression/Bounce.php
@@ -32,7 +32,7 @@ class Bounce extends HttpApi
      *
      * @return IndexResponse
      */
-    public function index($domain, $limit = 100)
+    public function index(string $domain, int $limit = 100)
     {
         Assert::stringNotEmpty($domain);
         Assert::range($limit, 1, 10000, '"Limit" parameter must be between 1 and 10000');
@@ -52,7 +52,7 @@ class Bounce extends HttpApi
      *
      * @return ShowResponse
      */
-    public function show($domain, $address)
+    public function show(string $domain, string $address)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -69,7 +69,7 @@ class Bounce extends HttpApi
      *
      * @return CreateResponse
      */
-    public function create($domain, $address, array $params = [])
+    public function create(string $domain, string $address, array $params = [])
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -87,7 +87,7 @@ class Bounce extends HttpApi
      *
      * @return DeleteResponse
      */
-    public function delete($domain, $address)
+    public function delete(string $domain, string $address)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -102,7 +102,7 @@ class Bounce extends HttpApi
      *
      * @return DeleteResponse
      */
-    public function deleteAll($domain)
+    public function deleteAll(string $domain)
     {
         Assert::stringNotEmpty($domain);
 
diff --git a/src/Api/Suppression/Complaint.php b/src/Api/Suppression/Complaint.php
index cd7a3d9..273ea0a 100644
--- a/src/Api/Suppression/Complaint.php
+++ b/src/Api/Suppression/Complaint.php
@@ -32,7 +32,7 @@ class Complaint extends HttpApi
      *
      * @return IndexResponse
      */
-    public function index($domain, $limit = 100)
+    public function index(string $domain, int $limit = 100)
     {
         Assert::stringNotEmpty($domain);
         Assert::range($limit, 1, 10000, 'Limit parameter must be between 1 and 10000');
@@ -52,7 +52,7 @@ class Complaint extends HttpApi
      *
      * @return ShowResponse
      */
-    public function show($domain, $address)
+    public function show(string $domain, string $address)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -68,7 +68,7 @@ class Complaint extends HttpApi
      *
      * @return CreateResponse
      */
-    public function create($domain, $address, $createdAt = null)
+    public function create(string $domain, string $address, string $createdAt = null)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -90,7 +90,7 @@ class Complaint extends HttpApi
      *
      * @return DeleteResponse
      */
-    public function delete($domain, $address)
+    public function delete(string $domain, string $address)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -105,7 +105,7 @@ class Complaint extends HttpApi
      *
      * @return DeleteResponse
      */
-    public function deleteAll($domain)
+    public function deleteAll(string $domain)
     {
         Assert::stringNotEmpty($domain);
 
diff --git a/src/Api/Suppression/Unsubscribe.php b/src/Api/Suppression/Unsubscribe.php
index b06a459..0b7a7e1 100644
--- a/src/Api/Suppression/Unsubscribe.php
+++ b/src/Api/Suppression/Unsubscribe.php
@@ -32,7 +32,7 @@ class Unsubscribe extends HttpApi
      *
      * @return IndexResponse
      */
-    public function index($domain, $limit = 100)
+    public function index(string $domain, int $limit = 100)
     {
         Assert::stringNotEmpty($domain);
         Assert::range($limit, 1, 10000, 'Limit parameter must be between 1 and 10000');
@@ -52,7 +52,7 @@ class Unsubscribe extends HttpApi
      *
      * @return ShowResponse
      */
-    public function show($domain, $address)
+    public function show(string $domain, string $address)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -69,7 +69,7 @@ class Unsubscribe extends HttpApi
      *
      * @return CreateResponse
      */
-    public function create($domain, $address, array $params = [])
+    public function create(string $domain, string $address, array $params = [])
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -87,7 +87,7 @@ class Unsubscribe extends HttpApi
      *
      * @return DeleteResponse
      */
-    public function delete($domain, $address)
+    public function delete(string $domain, string $address)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($address);
@@ -102,7 +102,7 @@ class Unsubscribe extends HttpApi
      *
      * @return DeleteResponse
      */
-    public function deleteAll($domain)
+    public function deleteAll(string $domain)
     {
         Assert::stringNotEmpty($domain);
 
diff --git a/src/Api/Tag.php b/src/Api/Tag.php
index 2befb99..6882d70 100644
--- a/src/Api/Tag.php
+++ b/src/Api/Tag.php
@@ -26,17 +26,13 @@ class Tag extends HttpApi
 {
     /**
      * Returns a list of tags.
-     *
-     * @param string $domain
-     * @param int    $limit
+
      *
      * @return IndexResponse|ResponseInterface
      */
-    public function index($domain, $limit = 100)
+    public function index(string $domain, int $limit = 100)
     {
         Assert::stringNotEmpty($domain);
-        Assert::integer($limit);
-
         $params = [
             'limit' => $limit,
         ];
@@ -49,12 +45,9 @@ class Tag extends HttpApi
     /**
      * Returns a single tag.
      *
-     * @param string $domain Name of the domain
-     * @param string $tag
-     *
      * @return ShowResponse|ResponseInterface
      */
-    public function show($domain, $tag)
+    public function show(string $domain, string $tag)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($tag);
@@ -67,17 +60,13 @@ class Tag extends HttpApi
     /**
      * Update a tag.
      *
-     * @param string $domain
-     * @param string $tag
-     * @param string $description
      *
      * @return UpdateResponse|ResponseInterface
      */
-    public function update($domain, $tag, $description)
+    public function update(string $domain, string $tag, string $description)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($tag);
-        Assert::string($description);
 
         $params = [
             'description' => $description,
@@ -91,17 +80,13 @@ class Tag extends HttpApi
     /**
      * Returns statistics for a single tag.
      *
-     * @param string $domain Name of the domain
-     * @param string $tag
-     * @param array  $params
      *
      * @return StatisticsResponse|ResponseInterface
      */
-    public function stats($domain, $tag, array $params)
+    public function stats(string $domain, string $tag, array $params)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($tag);
-        Assert::isArray($params);
 
         $response = $this->httpGet(sprintf('/v3/%s/tags/%s/stats', $domain, $tag), $params);
 
@@ -111,12 +96,10 @@ class Tag extends HttpApi
     /**
      * Removes a tag from the account.
      *
-     * @param string $domain Name of the domain
-     * @param string $tag
      *
      * @return DeleteResponse|ResponseInterface
      */
-    public function delete($domain, $tag)
+    public function delete(string $domain, string $tag)
     {
         Assert::stringNotEmpty($domain);
         Assert::stringNotEmpty($tag);
diff --git a/src/Api/Webhook.php b/src/Api/Webhook.php
index 9f16a02..4bf2b0a 100644
--- a/src/Api/Webhook.php
+++ b/src/Api/Webhook.php
@@ -17,7 +17,8 @@ use Mailgun\Model\Webhook\DeleteResponse;
 use Mailgun\Model\Webhook\IndexResponse;
 use Mailgun\Model\Webhook\ShowResponse;
 use Mailgun\Model\Webhook\UpdateResponse;
-use Mailgun\RequestBuilder;
+use Mailgun\HttpClient\RequestBuilder;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
@@ -29,13 +30,7 @@ class Webhook extends HttpApi
      */
     private $apiKey;
 
-    /**
-     * @param HttpClient     $httpClient
-     * @param RequestBuilder $requestBuilder
-     * @param Hydrator       $hydrator
-     * @param string         $apiKey
-     */
-    public function __construct(HttpClient $httpClient, RequestBuilder $requestBuilder, Hydrator $hydrator, $apiKey)
+    public function __construct(HttpClient $httpClient, RequestBuilder $requestBuilder, Hydrator $hydrator, string $apiKey)
     {
         parent::__construct($httpClient, $requestBuilder, $hydrator);
         $this->apiKey = $apiKey;
@@ -46,14 +41,8 @@ class Webhook extends HttpApi
      *
      * If this function returns FALSE, you must not process the request.
      * You should reject the request with status code 403 Forbidden.
-     *
-     * @param int    $timestamp
-     * @param string $token
-     * @param string $signature
-     *
-     * @return bool
      */
-    public function verifyWebhookSignature($timestamp, $token, $signature)
+    public function verifyWebhookSignature(int $timestamp, string $token, string $signature): bool
     {
         if (empty($timestamp) || empty($token) || empty($signature)) {
             return false;
@@ -70,11 +59,9 @@ class Webhook extends HttpApi
     }
 
     /**
-     * @param string $domain
-     *
-     * @return IndexResponse
+     * @return IndexResponse|ResponseInterface
      */
-    public function index($domain)
+    public function index(string $domain)
     {
         Assert::notEmpty($domain);
         $response = $this->httpGet(sprintf('/v3/domains/%s/webhooks', $domain));
@@ -83,12 +70,9 @@ class Webhook extends HttpApi
     }
 
     /**
-     * @param string $domain
-     * @param string $webhook
-     *
-     * @return ShowResponse
+     * @return ShowResponse|ResponseInterface
      */
-    public function show($domain, $webhook)
+    public function show(string $domain, string $webhook)
     {
         Assert::notEmpty($domain);
         Assert::notEmpty($webhook);
@@ -98,13 +82,9 @@ class Webhook extends HttpApi
     }
 
     /**
-     * @param string $domain
-     * @param string $id
-     * @param string $url
-     *
-     * @return CreateResponse
+     * @return CreateResponse|ResponseInterface
      */
-    public function create($domain, $id, $url)
+    public function create(string $domain, string $id, string $url)
     {
         Assert::notEmpty($domain);
         Assert::notEmpty($id);
@@ -121,13 +101,9 @@ class Webhook extends HttpApi
     }
 
     /**
-     * @param string $domain
-     * @param string $id
-     * @param string $url
-     *
-     * @return UpdateResponse
+     * @return UpdateResponse|ResponseInterface
      */
-    public function update($domain, $id, $url)
+    public function update(string $domain, string $id, string $url)
     {
         Assert::notEmpty($domain);
         Assert::notEmpty($id);
@@ -143,12 +119,9 @@ class Webhook extends HttpApi
     }
 
     /**
-     * @param string $domain
-     * @param string $id
-     *
-     * @return DeleteResponse
+     * @return DeleteResponse|ResponseInterface
      */
-    public function delete($domain, $id)
+    public function delete(string $domain, string $id)
     {
         Assert::notEmpty($domain);
         Assert::notEmpty($id);
diff --git a/src/Exception.php b/src/Exception.php
index bd98248..a0b34e4 100644
--- a/src/Exception.php
+++ b/src/Exception.php
@@ -14,6 +14,6 @@ namespace Mailgun;
  *
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  */
-interface Exception
+interface Exception extends \Throwable
 {
 }
diff --git a/src/Exception/HttpClientException.php b/src/Exception/HttpClientException.php
index da50873..bd32467 100644
--- a/src/Exception/HttpClientException.php
+++ b/src/Exception/HttpClientException.php
@@ -25,93 +25,73 @@ final class HttpClientException extends \RuntimeException implements Exception
     /**
      * @var array
      */
-    private $responseBody;
+    private $responseBody = [];
 
     /**
      * @var int
      */
     private $responseCode;
 
-    /**
-     * @param string                 $message
-     * @param int                    $code
-     * @param ResponseInterface|null $response
-     */
-    public function __construct($message, $code, ResponseInterface $response = null)
+    public function __construct(string $message, int $code, ResponseInterface $response)
     {
         parent::__construct($message, $code);
 
-        if ($response) {
-            $this->response = $response;
-            $this->responseCode = $response->getStatusCode();
-            $body = $response->getBody()->__toString();
-            if (0 !== strpos($response->getHeaderLine('Content-Type'), 'application/json')) {
-                $this->responseBody['message'] = $body;
-            } else {
-                $this->responseBody = json_decode($body, true);
-            }
+        $this->response = $response;
+        $this->responseCode = $response->getStatusCode();
+        $body = $response->getBody()->__toString();
+        if (0 !== strpos($response->getHeaderLine('Content-Type'), 'application/json')) {
+            $this->responseBody['message'] = $body;
+        } else {
+            $this->responseBody = json_decode($body, true);
         }
     }
 
-    public static function badRequest(ResponseInterface $response = null)
+    public static function badRequest(ResponseInterface $response)
     {
-        $message = 'The parameters passed to the API were invalid. Check your inputs!';
-
-        if (null !== $response) {
-            $body = $response->getBody()->__toString();
-            if (0 !== strpos($response->getHeaderLine('Content-Type'), 'application/json')) {
-                $validationMessage = $body;
-            } else {
-                $jsonDecoded = json_decode($body, true);
-                $validationMessage = isset($jsonDecoded['message']) ? $jsonDecoded['message'] : $body;
-            }
-
-            $message = sprintf("%s\n\n%s", $message, $validationMessage);
+        $body = $response->getBody()->__toString();
+        if (0 !== strpos($response->getHeaderLine('Content-Type'), 'application/json')) {
+            $validationMessage = $body;
+        } else {
+            $jsonDecoded = json_decode($body, true);
+            $validationMessage = isset($jsonDecoded['message']) ? $jsonDecoded['message'] : $body;
         }
 
+        $message = sprintf("The parameters passed to the API were invalid. Check your inputs!\n\n%s", $validationMessage);
+
         return new self($message, 400, $response);
     }
 
-    public static function unauthorized(ResponseInterface $response = null)
+    public static function unauthorized(ResponseInterface $response)
     {
         return new self('Your credentials are incorrect.', 401, $response);
     }
 
-    public static function requestFailed(ResponseInterface $response = null)
+    public static function requestFailed(ResponseInterface $response)
     {
         return new self('Parameters were valid but request failed. Try again.', 402, $response);
     }
 
-    public static function notFound(ResponseInterface $response = null)
+    public static function notFound(ResponseInterface $response)
     {
         return new self('The endpoint you have tried to access does not exist. Check if the domain matches the domain you have configure on Mailgun.', 404, $response);
     }
 
-    public static function payloadTooLarge(ResponseInterface $response = null)
+    public static function payloadTooLarge(ResponseInterface $response)
     {
         return new self('Payload too large, your total attachment size is too big.', 413, $response);
     }
 
-    /**
-     * @return ResponseInterface
-     */
-    public function getResponse()
+    public function getResponse(): ?ResponseInterface
     {
         return $this->response;
     }
 
-    /**
-     * @return array
-     */
-    public function getResponseBody()
+    public function getResponseBody(): array
     {
         return $this->responseBody;
     }
 
-    /**
-     * @return int
-     */
-    public function getResponseCode()
+    public function getResponseCode(): int
     {
         return $this->responseCode;
     }
diff --git a/src/Exception/HttpServerException.php b/src/Exception/HttpServerException.php
index 857b648..ff701d5 100644
--- a/src/Exception/HttpServerException.php
+++ b/src/Exception/HttpServerException.php
@@ -16,7 +16,7 @@ use Mailgun\Exception;
  */
 final class HttpServerException extends \RuntimeException implements Exception
 {
-    public static function serverError($httpStatus = 500)
+    public static function serverError(int $httpStatus = 500)
     {
         return new self('An unexpected error occurred at Mailgun\'s servers. Try again later and contact support if the error still exists.', $httpStatus);
     }
@@ -26,7 +26,7 @@ final class HttpServerException extends \RuntimeException implements Exception
         return new self('Mailgun\'s servers are currently unreachable.', 0, $previous);
     }
 
-    public static function unknownHttpResponseCode($code)
+    public static function unknownHttpResponseCode(int $code)
     {
         return new self(sprintf('Unknown HTTP response code ("%d") received from the API server', $code));
     }
diff --git a/src/HttpClientConfigurator.php b/src/HttpClient/HttpClientConfigurator.php
similarity index 70%
rename from src/HttpClientConfigurator.php
rename to src/HttpClient/HttpClientConfigurator.php
index d08315d..cf74a12 100644
--- a/src/HttpClientConfigurator.php
+++ b/src/HttpClient/HttpClientConfigurator.php
@@ -7,7 +7,7 @@
  * of the MIT license. See the LICENSE file for details.
  */
 
-namespace Mailgun;
+namespace Mailgun\HttpClient;
 
 use Http\Client\HttpClient;
 use Http\Client\Common\PluginClient;
@@ -62,10 +62,7 @@ final class HttpClientConfigurator
         $this->responseHistory = new History();
     }
 
-    /**
-     * @return PluginClient
-     */
-    public function createConfiguredClient()
+    public function createConfiguredClient(): PluginClient
     {
         $plugins = [
             new Plugin\AddHostPlugin($this->getUriFactory()->createUri($this->endpoint)),
@@ -83,54 +80,33 @@ final class HttpClientConfigurator
         return new PluginClient($this->getHttpClient(), $plugins);
     }
 
-    /**
-     * @param bool $debug
-     *
-     * @return HttpClientConfigurator
-     */
-    public function setDebug($debug)
+    public function setDebug(bool $debug): self
     {
         $this->debug = $debug;
 
         return $this;
     }
 
-    /**
-     * @param string $endpoint
-     *
-     * @return HttpClientConfigurator
-     */
-    public function setEndpoint($endpoint)
+    public function setEndpoint(string $endpoint): self
     {
         $this->endpoint = $endpoint;
 
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getApiKey()
+    public function getApiKey(): string
     {
         return $this->apiKey;
     }
 
-    /**
-     * @param string $apiKey
-     *
-     * @return HttpClientConfigurator
-     */
-    public function setApiKey($apiKey)
+    public function setApiKey(string $apiKey): self
     {
         $this->apiKey = $apiKey;
 
         return $this;
     }
 
-    /**
-     * @return UriFactory
-     */
-    private function getUriFactory()
+    private function getUriFactory(): UriFactory
     {
         if (null === $this->uriFactory) {
             $this->uriFactory = UriFactoryDiscovery::find();
@@ -139,22 +115,14 @@ final class HttpClientConfigurator
         return $this->uriFactory;
     }
 
-    /**
-     * @param UriFactory $uriFactory
-     *
-     * @return HttpClientConfigurator
-     */
-    public function setUriFactory(UriFactory $uriFactory)
+    public function setUriFactory(UriFactory $uriFactory): self
     {
         $this->uriFactory = $uriFactory;
 
         return $this;
     }
 
-    /**
-     * @return HttpClient
-     */
-    private function getHttpClient()
+    private function getHttpClient(): HttpClient
     {
         if (null === $this->httpClient) {
             $this->httpClient = HttpClientDiscovery::find();
@@ -163,22 +131,14 @@ final class HttpClientConfigurator
         return $this->httpClient;
     }
 
-    /**
-     * @param HttpClient $httpClient
-     *
-     * @return HttpClientConfigurator
-     */
-    public function setHttpClient(HttpClient $httpClient)
+    public function setHttpClient(HttpClient $httpClient): self
     {
         $this->httpClient = $httpClient;
 
         return $this;
     }
 
-    /**
-     * @return History
-     */
-    public function getResponseHistory()
+    public function getResponseHistory(): History
     {
         return $this->responseHistory;
     }
diff --git a/src/RequestBuilder.php b/src/HttpClient/RequestBuilder.php
similarity index 96%
rename from src/RequestBuilder.php
rename to src/HttpClient/RequestBuilder.php
index df355f3..4027c80 100644
--- a/src/RequestBuilder.php
+++ b/src/HttpClient/RequestBuilder.php
@@ -7,7 +7,7 @@
  * of the MIT license. See the LICENSE file for details.
  */
 
-namespace Mailgun;
+namespace Mailgun\HttpClient;
 
 use Http\Discovery\MessageFactoryDiscovery;
 use Http\Message\MultipartStream\MultipartStreamBuilder;
@@ -46,7 +46,7 @@ class RequestBuilder
      *
      * @return RequestInterface
      */
-    public function create($method, $uri, array $headers = [], $body = null)
+    public function create(string $method, string $uri, array $headers = [], $body = null)
     {
         if (!is_array($body)) {
             return $this->getRequestFactory()->createRequest($method, $uri, $headers, $body);
diff --git a/src/Hydrator/ArrayHydrator.php b/src/Hydrator/ArrayHydrator.php
index cbb1d17..80f00e7 100644
--- a/src/Hydrator/ArrayHydrator.php
+++ b/src/Hydrator/ArrayHydrator.php
@@ -20,12 +20,9 @@ use Psr\Http\Message\ResponseInterface;
 final class ArrayHydrator implements Hydrator
 {
     /**
-     * @param ResponseInterface $response
-     * @param string            $class
-     *
      * @return array
      */
-    public function hydrate(ResponseInterface $response, $class)
+    public function hydrate(ResponseInterface $response, string $class)
     {
         $body = $response->getBody()->__toString();
         if (0 !== strpos($response->getHeaderLine('Content-Type'), 'application/json')) {
diff --git a/src/Hydrator/Hydrator.php b/src/Hydrator/Hydrator.php
index 314db97..6eedba7 100644
--- a/src/Hydrator/Hydrator.php
+++ b/src/Hydrator/Hydrator.php
@@ -18,12 +18,9 @@ use Psr\Http\Message\ResponseInterface;
 interface Hydrator
 {
     /**
-     * @param ResponseInterface $response
-     * @param string            $class
-     *
      * @return mixed
      *
      * @throws HydrationException
      */
-    public function hydrate(ResponseInterface $response, $class);
+    public function hydrate(ResponseInterface $response, string $class);
 }
diff --git a/src/Hydrator/ModelHydrator.php b/src/Hydrator/ModelHydrator.php
index 2e964e6..f8be980 100644
--- a/src/Hydrator/ModelHydrator.php
+++ b/src/Hydrator/ModelHydrator.php
@@ -21,12 +21,9 @@ use Psr\Http\Message\ResponseInterface;
 final class ModelHydrator implements Hydrator
 {
     /**
-     * @param ResponseInterface $response
-     * @param string            $class
-     *
      * @return ResponseInterface
      */
-    public function hydrate(ResponseInterface $response, $class)
+    public function hydrate(ResponseInterface $response, string $class)
     {
         $body = $response->getBody()->__toString();
         $contentType = $response->getHeaderLine('Content-Type');
diff --git a/src/Hydrator/NoopHydrator.php b/src/Hydrator/NoopHydrator.php
index 2f82fb9..0d8afb2 100644
--- a/src/Hydrator/NoopHydrator.php
+++ b/src/Hydrator/NoopHydrator.php
@@ -19,12 +19,9 @@ use Psr\Http\Message\ResponseInterface;
 final class NoopHydrator implements Hydrator
 {
     /**
-     * @param ResponseInterface $response
-     * @param string            $class
-     *
      * @throws \LogicException
      */
-    public function hydrate(ResponseInterface $response, $class)
+    public function hydrate(ResponseInterface $response, string $class)
     {
         throw new \LogicException('The NoopHydrator should never be called');
     }
diff --git a/src/Mailgun.php b/src/Mailgun.php
index c828601..dac2a3f 100644
--- a/src/Mailgun.php
+++ b/src/Mailgun.php
@@ -77,74 +77,52 @@ final class Mailgun
         return $this->responseHistory->getLastResponse();
     }
 
-    /**
-     * @return Api\Stats
-     */
-    public function stats()
+    public function stats(): Api\Stats
     {
         return new Api\Stats($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Api\Attachment
-     */
-    public function attachment()
+    public function attachment(): Api\Attachment
     {
         return new Api\Attachment($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Api\Domain
-     */
-    public function domains()
+    public function domains(): Api\Domain
     {
         return new Api\Domain($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Api\Tag
-     */
-    public function tags()
+    public function tags(): Api\Tag
     {
         return new Api\Tag($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Api\Event
-     */
-    public function events()
+    public function events(): Api\Event
     {
         return new Api\Event($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Api\Route
-     */
-    public function routes()
+    public function routes(): Api\Route
     {
         return new Api\Route($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Api\Webhook
-     */
-    public function webhooks()
+    public function webhooks(): Api\Webhook
     {
         return new Api\Webhook($this->httpClient, $this->requestBuilder, $this->hydrator, $this->apiKey);
     }
 
-    /**
-     * @return Api\Message
-     */
-    public function messages()
+    public function messages(): Api\Message
     {
         return new Api\Message($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
 
-    /**
-     * @return Api\Suppression
-     */
-    public function suppressions()
+    public function ips(): Api\Ip
+    {
+        return new Api\Ip($this->httpClient, $this->requestBuilder, $this->hydrator);
+    }
+
+    public function suppressions(): Api\Suppression
     {
         return new Api\Suppression($this->httpClient, $this->requestBuilder, $this->hydrator);
     }
diff --git a/src/Message/BatchMessage.php b/src/Message/BatchMessage.php
index 8c48c4e..5392bc8 100644
--- a/src/Message/BatchMessage.php
+++ b/src/Message/BatchMessage.php
@@ -30,7 +30,7 @@ class BatchMessage extends MessageBuilder
     /**
      * @var bool
      */
-    private $autoSend = true;
+    private $autoSend;
 
     /**
      * @var array
@@ -47,12 +47,7 @@ class BatchMessage extends MessageBuilder
      */
     private $api;
 
-    /**
-     * @param Message $messageApi
-     * @param string  $domain
-     * @param bool    $autoSend
-     */
-    public function __construct(Message $messageApi, $domain, $autoSend)
+    public function __construct(Message $messageApi, string $domain, bool $autoSend)
     {
         $this->api = $messageApi;
         $this->domain = $domain;
@@ -72,10 +67,8 @@ class BatchMessage extends MessageBuilder
      *
      * @throws MissingRequiredParameter
      * @throws TooManyRecipients
-     *
-     * @return BatchMessage
      */
-    protected function addRecipient($headerName, $address, array $variables)
+    protected function addRecipient(string $headerName, string $address, array $variables): MessageBuilder
     {
         if (array_key_exists($headerName, $this->counters['recipients'])) {
             if (self::RECIPIENT_COUNT_LIMIT === $this->counters['recipients'][$headerName]) {
@@ -101,7 +94,7 @@ class BatchMessage extends MessageBuilder
      * @throws RuntimeException
      * @throws MissingRequiredParameter
      */
-    public function finalize()
+    public function finalize(): void
     {
         $message = $this->message;
 
@@ -132,7 +125,7 @@ class BatchMessage extends MessageBuilder
     /**
      * @return string[]
      */
-    public function getMessageIds()
+    public function getMessageIds(): array
     {
         return $this->messageIds;
     }
diff --git a/src/Message/Exceptions/LimitExceeded.php b/src/Message/Exceptions/LimitExceeded.php
index e034eb7..4463d1d 100644
--- a/src/Message/Exceptions/LimitExceeded.php
+++ b/src/Message/Exceptions/LimitExceeded.php
@@ -13,7 +13,7 @@ use Mailgun\Exception;
 
 class LimitExceeded extends \Exception implements Exception
 {
-    public static function create($field, $limit)
+    public static function create(string $field, int $limit)
     {
         return new self(sprintf('You\'ve exceeded the maximum (%d) %s for a single message.', $limit, $field));
     }
diff --git a/src/Message/Exceptions/MissingRequiredParameter.php b/src/Message/Exceptions/MissingRequiredParameter.php
index cc2c350..832d5c8 100644
--- a/src/Message/Exceptions/MissingRequiredParameter.php
+++ b/src/Message/Exceptions/MissingRequiredParameter.php
@@ -13,7 +13,7 @@ use Mailgun\Exception;
 
 class MissingRequiredParameter extends \Exception implements Exception
 {
-    public static function create($parameter, $message = null)
+    public static function create(string $parameter, string $message = null)
     {
         if (null === $message) {
             $message = 'The parameters passed to the API were invalid. Please specify "%s".';
diff --git a/src/Message/Exceptions/TooManyRecipients.php b/src/Message/Exceptions/TooManyRecipients.php
index 336c885..a2bdaca 100644
--- a/src/Message/Exceptions/TooManyRecipients.php
+++ b/src/Message/Exceptions/TooManyRecipients.php
@@ -14,12 +14,12 @@ use Mailgun\Message\MessageBuilder;
 
 class TooManyRecipients extends LimitExceeded implements Exception
 {
-    public static function create($field, $limit = MessageBuilder::RECIPIENT_COUNT_LIMIT)
+    public static function create(string $field, int $limit = MessageBuilder::RECIPIENT_COUNT_LIMIT)
     {
         return new self(sprintf('You\'ve exceeded the maximum recipient count (%s) for filed "%s".', $limit, $field));
     }
 
-    public static function whenAutoSendDisabled($limit = MessageBuilder::RECIPIENT_COUNT_LIMIT)
+    public static function whenAutoSendDisabled(int $limit = MessageBuilder::RECIPIENT_COUNT_LIMIT)
     {
         return new self(sprintf('You\'ve exceeded the maximum recipient count (%s) with autosend disabled.', $limit));
     }
diff --git a/src/Message/MessageBuilder.php b/src/Message/MessageBuilder.php
index 4fe52e9..5385ebf 100644
--- a/src/Message/MessageBuilder.php
+++ b/src/Message/MessageBuilder.php
@@ -62,7 +62,7 @@ class MessageBuilder
      *
      * @return mixed
      */
-    private function get($params, $key, $default)
+    private function get(array $params, string $key, $default)
     {
         if (array_key_exists($key, $params)) {
             return $params[$key];
@@ -78,10 +78,8 @@ class MessageBuilder
      *     @var string $first
      *     @var string $last
      * }
-     *
-     * @return string
      */
-    private function getFullName(array $params)
+    private function getFullName(array $params): string
     {
         if (isset($params['full_name'])) {
             return $this->get($params, 'full_name', '');
@@ -98,10 +96,8 @@ class MessageBuilder
      *     @var string $first
      *     @var string $last
      * }
-     *
-     * @return string
      */
-    protected function parseAddress($address, array $variables)
+    protected function parseAddress(string $address, array $variables): string
     {
         $fullName = $this->getFullName($variables);
         if (!empty($fullName)) {
@@ -120,10 +116,8 @@ class MessageBuilder
      *     @var string $first
      *     @var string $last
      * }
-     *
-     * @return MessageBuilder
      */
-    protected function addRecipient($headerName, $address, array $variables)
+    protected function addRecipient(string $headerName, string $address, array $variables): self
     {
         $compiledAddress = $this->parseAddress($address, $variables);
 
@@ -152,10 +146,8 @@ class MessageBuilder
      * }
      *
      * @throws TooManyRecipients
-     *
-     * @return MessageBuilder
      */
-    public function addToRecipient($address, array $variables = [])
+    public function addToRecipient(string $address, array $variables = []): self
     {
         if ($this->counters['recipients']['to'] > self::RECIPIENT_COUNT_LIMIT) {
             throw TooManyRecipients::create('to');
@@ -176,10 +168,8 @@ class MessageBuilder
      * }
      *
      * @throws TooManyRecipients
-     *
-     * @return MessageBuilder
      */
-    public function addCcRecipient($address, array $variables = [])
+    public function addCcRecipient(string $address, array $variables = []): self
     {
         if ($this->counters['recipients']['cc'] > self::RECIPIENT_COUNT_LIMIT) {
             throw TooManyRecipients::create('cc');
@@ -201,10 +191,8 @@ class MessageBuilder
      * }
      *
      * @throws TooManyRecipients
-     *
-     * @return MessageBuilder
      */
-    public function addBccRecipient($address, array $variables = [])
+    public function addBccRecipient(string $address, array $variables = []): self
     {
         if ($this->counters['recipients']['bcc'] > self::RECIPIENT_COUNT_LIMIT) {
             throw TooManyRecipients::create('bcc');
@@ -224,10 +212,8 @@ class MessageBuilder
      *     @var string $first
      *     @var string $last
      * }
-     *
-     * @return MessageBuilder
      */
-    public function setFromAddress($address, array $variables = [])
+    public function setFromAddress(string $address, array $variables = []): self
     {
         $this->addRecipient('from', $address, $variables);
 
@@ -243,22 +229,15 @@ class MessageBuilder
      *     @var string $first
      *     @var string $last
      * }
-     *
-     * @return MessageBuilder
      */
-    public function setReplyToAddress($address, array $variables = [])
+    public function setReplyToAddress(string $address, array $variables = []): self
     {
         $this->addRecipient('h:reply-to', $address, $variables);
 
         return $this;
     }
 
-    /**
-     * @param string $subject
-     *
-     * @return MessageBuilder
-     */
-    public function setSubject($subject)
+    public function setSubject(string $subject): self
     {
         $this->message['subject'] = $subject;
 
@@ -268,10 +247,8 @@ class MessageBuilder
     /**
      * @param string $headerName
      * @param mixed  $headerData
-     *
-     * @return MessageBuilder
      */
-    public function addCustomHeader($headerName, $headerData)
+    public function addCustomHeader(string $headerName, $headerData): self
     {
         if (!preg_match('/^h:/i', $headerName)) {
             $headerName = 'h:'.$headerName;
@@ -290,37 +267,21 @@ class MessageBuilder
         return $this;
     }
 
-    /**
-     * @param string $textBody
-     *
-     * @return MessageBuilder
-     */
-    public function setTextBody($textBody)
+    public function setTextBody(string $textBody): self
     {
         $this->message['text'] = $textBody;
 
         return $this;
     }
 
-    /**
-     * @param string $htmlBody
-     *
-     * @return MessageBuilder
-     */
-    public function setHtmlBody($htmlBody)
+    public function setHtmlBody(string $htmlBody): self
     {
         $this->message['html'] = $htmlBody;
 
         return $this;
     }
 
-    /**
-     * @param string      $attachmentPath
-     * @param string|null $attachmentName
-     *
-     * @return MessageBuilder
-     */
-    public function addAttachment($attachmentPath, $attachmentName = null)
+    public function addAttachment(string $attachmentPath, string $attachmentName = null): self
     {
         if (!isset($this->message['attachment'])) {
             $this->message['attachment'] = [];
@@ -334,13 +295,7 @@ class MessageBuilder
         return $this;
     }
 
-    /**
-     * @param string      $inlineImagePath
-     * @param string|null $inlineImageName
-     *
-     * @return MessageBuilder
-     */
-    public function addInlineImage($inlineImagePath, $inlineImageName = null)
+    public function addInlineImage(string $inlineImagePath, string $inlineImageName = null): self
     {
         if (!isset($this->message['inline'])) {
             $this->message['inline'] = [];
@@ -354,26 +309,17 @@ class MessageBuilder
         return $this;
     }
 
-    /**
-     * @param bool $enabled
-     *
-     * @return MessageBuilder
-     */
-    public function setTestMode($enabled)
+    public function setTestMode(bool $enabled): self
     {
-        $this->message['o:testmode'] = $this->boolToString($enabled);
+        $this->message['o:testmode'] = $enabled ? 'yes' : 'no';
 
         return $this;
     }
 
     /**
-     * @param string $campaignId
-     *
      * @throws LimitExceeded
-     *
-     * @return MessageBuilder
      */
-    public function addCampaignId($campaignId)
+    public function addCampaignId(string $campaignId): self
     {
         if ($this->counters['attributes']['campaign_id'] >= self::CAMPAIGN_ID_LIMIT) {
             throw LimitExceeded::create('campaigns', self::CAMPAIGN_ID_LIMIT);
@@ -389,13 +335,9 @@ class MessageBuilder
     }
 
     /**
-     * @param string $tag
-     *
      * @throws LimitExceeded
-     *
-     * @return MessageBuilder
      */
-    public function addTag($tag)
+    public function addTag(string $tag): self
     {
         if ($this->counters['attributes']['tag'] >= self::TAG_LIMIT) {
             throw LimitExceeded::create('tags', self::TAG_LIMIT);
@@ -411,49 +353,36 @@ class MessageBuilder
         return $this;
     }
 
-    /**
-     * @param bool $enabled
-     *
-     * @return MessageBuilder
-     */
-    public function setDkim($enabled)
+    public function setDkim(bool $enabled): self
     {
-        $this->message['o:dkim'] = $this->boolToString($enabled);
+        $this->message['o:dkim'] = $enabled ? 'yes' : 'no';
 
         return $this;
     }
 
-    /**
-     * @param bool $enabled
-     *
-     * @return MessageBuilder
-     */
-    public function setOpenTracking($enabled)
+    public function setOpenTracking(bool $enabled): self
     {
-        $this->message['o:tracking-opens'] = $this->boolToString($enabled);
+        $this->message['o:tracking-opens'] = $enabled ? 'yes' : 'no';
 
         return $this;
     }
 
-    /**
-     * @param bool $enabled
-     *
-     * @return MessageBuilder
-     */
-    public function setClickTracking($enabled)
+    public function setClickTracking(bool $enabled, bool $htmlOnly = false): self
     {
-        $this->message['o:tracking-clicks'] = $this->boolToString($enabled);
+        $value = 'no';
+        if ($enabled) {
+            $value = 'yes';
+            if ($htmlOnly) {
+                $value = 'htmlonly';
+            }
+        }
+
+        $this->message['o:tracking-clicks'] = $value;
 
         return $this;
     }
 
-    /**
-     * @param string      $timeDate
-     * @param string|null $timeZone
-     *
-     * @return MessageBuilder
-     */
-    public function setDeliveryTime($timeDate, $timeZone = null)
+    public function setDeliveryTime(string $timeDate, string $timeZone = null): self
     {
         if (null !== $timeZone) {
             $timeZoneObj = new \DateTimeZone($timeZone);
@@ -471,10 +400,8 @@ class MessageBuilder
     /**
      * @param string $customName
      * @param mixed  $data
-     *
-     * @return MessageBuilder
      */
-    public function addCustomData($customName, $data)
+    public function addCustomData(string $customName, $data): self
     {
         $this->message['v:'.$customName] = json_encode($data);
 
@@ -484,10 +411,8 @@ class MessageBuilder
     /**
      * @param string $parameterName
      * @param mixed  $data
-     *
-     * @return MessageBuilder
      */
-    public function addCustomParameter($parameterName, $data)
+    public function addCustomParameter(string $parameterName, $data): self
     {
         if (isset($this->message[$parameterName])) {
             $this->message[$parameterName][] = $data;
@@ -498,41 +423,15 @@ class MessageBuilder
         return $this;
     }
 
-    /**
-     * @param array $message
-     *
-     * @return MessageBuilder
-     */
-    public function setMessage($message)
+    public function setMessage(array $message): self
     {
         $this->message = $message;
 
         return $this;
     }
 
-    /**
-     * @return array
-     */
-    public function getMessage()
+    public function getMessage(): array
     {
         return $this->message;
     }
-
-    /**
-     * @param $enabled
-     *
-     * @return string
-     */
-    private function boolToString($enabled)
-    {
-        if (filter_var($enabled, FILTER_VALIDATE_BOOLEAN)) {
-            $enabled = 'yes';
-        } elseif ('html' === $enabled) {
-            $enabled = 'html';
-        } else {
-            $enabled = 'no';
-        }
-
-        return $enabled;
-    }
 }
diff --git a/tests/Api/MailingList/MemberTest.php b/tests/Api/MailingList/MemberTest.php
index cc8f0ae..1fd918f 100644
--- a/tests/Api/MailingList/MemberTest.php
+++ b/tests/Api/MailingList/MemberTest.php
@@ -20,7 +20,6 @@ class MemberTest extends TestCase
     {
         $data = [
             'limit' => 100,
-            'subscribed' => null,
         ];
 
         $api = $this->getApiMock();
@@ -45,7 +44,7 @@ class MemberTest extends TestCase
             ->with('/v3/lists/address/members/pages', $data)
             ->willReturn(new Response());
 
-        $api->index('address', 100, 'yes');
+        $api->index('address', 100, true);
     }
 
     public function testIndexUnsubscribed()
@@ -61,7 +60,7 @@ class MemberTest extends TestCase
             ->with('/v3/lists/address/members/pages', $data)
             ->willReturn(new Response());
 
-        $api->index('address', 100, 'no');
+        $api->index('address', 100, false);
     }
 
     public function testCreate()
@@ -80,23 +79,21 @@ class MemberTest extends TestCase
             ->with('/v3/lists/address/members', $data)
             ->willReturn(new Response());
 
-        $api->create($list = 'address', $address = 'foo@example.com', $name = 'Foo', $vars = [], $subscribed = 'yes', $upsert = 'no');
+        $api->create($list = 'address', $address = 'foo@example.com', $name = 'Foo', $vars = [], $subscribed = true, $upsert = false);
     }
 
     public function testCreateInvalidAddress()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
-
         $api = $this->getApiMock();
+        $this->expectException(InvalidArgumentException::class);
         $api->create('address', '');
     }
 
     public function testCreateInvalidSubscribed()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
-
         $api = $this->getApiMock();
-        $api->create('address', 'foo@example.com', null, [], true);
+        $this->expectException(InvalidArgumentException::class);
+        $api->create('', 'foo@example.com');
     }
 
     public function testCreateMultiple()
@@ -128,12 +125,12 @@ class MemberTest extends TestCase
                 'name' => 'Billy',
                 'subscribed' => 'yes',
             ],
-        ], $upsert = 'no');
+        ], false);
     }
 
     public function testCreateMultipleInvalidMemberArgument()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
 
         $data = [
             'bob@example.com',
@@ -151,7 +148,7 @@ class MemberTest extends TestCase
 
     public function testCreateMultipleCountMax1000()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
 
         $members = range(1, 1001);
         $members = array_map('strval', $members);
@@ -180,7 +177,7 @@ class MemberTest extends TestCase
 
     public function testUpdateInvalidArgument()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
 
         $data = [
             'vars' => 'foo=bar',
diff --git a/tests/Api/MailingListTest.php b/tests/Api/MailingListTest.php
index 6fe4115..a646f8c 100644
--- a/tests/Api/MailingListTest.php
+++ b/tests/Api/MailingListTest.php
@@ -32,7 +32,7 @@ class MailingListTest extends TestCase
 
     public function testPagesInvalidArgument()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
         $api = $this->getApiMock();
         $limit = -1;
 
@@ -59,7 +59,7 @@ class MailingListTest extends TestCase
 
     public function testCreateInvalidAddress()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
 
         $api = $this->getApiMock();
         $api->create($address = '', $name = 'Foo', $description = 'Description', $accessLevel = 'readonly');
@@ -67,7 +67,7 @@ class MailingListTest extends TestCase
 
     public function testCreateInvalidAccessLevel()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
 
         $api = $this->getApiMock();
         $api->create($address = '', $name = 'Foo', $description = 'Description', $accessLevel = 'admin');
@@ -86,7 +86,7 @@ class MailingListTest extends TestCase
 
     public function testShowInvalidAddress()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
 
         $api = $this->getApiMock();
         $api->show('');
@@ -109,7 +109,7 @@ class MailingListTest extends TestCase
 
     public function testUpdateInvalidArgument()
     {
-        $this->setExpectedException(InvalidArgumentException::class);
+        $this->expectException(InvalidArgumentException::class);
 
         $data = [
             'access_level' => 'foo',
diff --git a/tests/Api/TestCase.php b/tests/Api/TestCase.php
index f2a7976..a85fea3 100644
--- a/tests/Api/TestCase.php
+++ b/tests/Api/TestCase.php
@@ -12,14 +12,13 @@ namespace Mailgun\Tests\Api;
 use GuzzleHttp\Psr7\Request;
 use GuzzleHttp\Psr7\Response;
 use Mailgun\Hydrator\ModelHydrator;
-use Mailgun\Mailgun;
 use Psr\Http\Message\ResponseInterface;
 
 /**
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
  * @author Contributors of https://github.com/KnpLabs/php-github-api
  */
-abstract class TestCase extends \PHPUnit_Framework_TestCase
+abstract class TestCase extends \PHPUnit\Framework\TestCase
 {
     private $requestMethod;
 
@@ -56,7 +55,7 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
                 ->method('sendRequest');
         }
         if (null === $requestClient) {
-            $requestClient = $this->getMockBuilder('Mailgun\RequestBuilder')
+            $requestClient = $this->getMockBuilder('Mailgun\HttpClient\RequestBuilder')
                 ->setMethods(['create'])
                 ->getMock();
         }
@@ -85,7 +84,7 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
             ->method('sendRequest')
             ->willReturn(null === $this->httpResponse ? new Response() : $this->httpResponse);
 
-        $requestClient = $this->getMockBuilder('Mailgun\RequestBuilder')
+        $requestClient = $this->getMockBuilder('Mailgun\HttpClient\RequestBuilder')
             ->setMethods(['create'])
             ->getMock();
         $requestClient->method('create')
@@ -255,22 +254,4 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
 
         return is_callable($property) ? call_user_func($property, $value) : $value === $property;
     }
-
-    /**
-     * Make sure expectException always exists, even on PHPUnit 4.
-     *
-     * @param string      $exception
-     * @param string|null $message
-     */
-    public function expectException($exception, $message = null)
-    {
-        if (method_exists($this, 'setExpectedException')) {
-            $this->setExpectedException($exception, $message);
-        } else {
-            parent::expectException($exception);
-            if (null !== $message) {
-                $this->expectExceptionMessage($message);
-            }
-        }
-    }
 }
diff --git a/tests/Api/WebhookTest.php b/tests/Api/WebhookTest.php
index 2c05321..c581d0e 100644
--- a/tests/Api/WebhookTest.php
+++ b/tests/Api/WebhookTest.php
@@ -48,7 +48,7 @@ class WebhookTest extends TestCase
     {
         $api = $this->getApiInstance('key-3ax6xnjp29jd6fds4gc373sgvjxteol0');
 
-        $this->assertFalse($api->verifyWebhookSignature('', '', ''));
+        $this->assertFalse($api->verifyWebhookSignature(0, '', ''));
     }
 
     public function testIndex()
diff --git a/tests/RequestBuilderTest.php b/tests/HttpClient/RequestBuilderTest.php
similarity index 90%
rename from tests/RequestBuilderTest.php
rename to tests/HttpClient/RequestBuilderTest.php
index 452eeef..882a237 100644
--- a/tests/RequestBuilderTest.php
+++ b/tests/HttpClient/RequestBuilderTest.php
@@ -7,17 +7,17 @@
  * of the MIT license. See the LICENSE file for details.
  */
 
-namespace Mailgun\Tests;
+namespace Mailgun\Tests\HttpClient;
 
 use Http\Message\MultipartStream\MultipartStreamBuilder;
 use Http\Message\RequestFactory;
-use Mailgun\RequestBuilder;
-use PHPUnit_Framework_MockObject_MockObject as MockObject;
-use PHPUnit_Framework_TestCase;
+use Mailgun\HttpClient\RequestBuilder;
+use Mailgun\Tests\MailgunTestCase;
+use PHPUnit\Framework\MockObject\MockObject;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\StreamInterface;
 
-class RequestBuilderTest extends PHPUnit_Framework_TestCase
+class RequestBuilderTest extends MailgunTestCase
 {
     /**
      * @var MockObject|RequestFactory
@@ -72,7 +72,7 @@ class RequestBuilderTest extends PHPUnit_Framework_TestCase
                 }),
                 $this->equalTo('content')
             )
-            ->willReturn($request = $this->getMock(RequestInterface::class));
+            ->willReturn($request = $this->getMockBuilder(RequestInterface::class)->getMock());
 
         $result = $this->requestBuilder
             ->create('GET', 'http://foo.bar', ['Content-Type' => 'application/json'], 'content');
@@ -108,7 +108,7 @@ class RequestBuilderTest extends PHPUnit_Framework_TestCase
         $multipartStreamBuilder
             ->expects($this->once())
             ->method('build')
-            ->willReturn($stream = $this->getMock(StreamInterface::class));
+            ->willReturn($stream = $this->getMockBuilder(StreamInterface::class)->getMock());
 
         $multipartStreamBuilder
             ->expects($this->once())
@@ -134,7 +134,7 @@ class RequestBuilderTest extends PHPUnit_Framework_TestCase
                 }),
                 $this->equalTo($stream)
             )
-            ->willReturn($request = $this->getMock(RequestInterface::class));
+            ->willReturn($request = $this->getMockBuilder(RequestInterface::class)->getMock());
 
         $this->requestBuilder->setMultipartStreamBuilder($multipartStreamBuilder);
         $result = $this->requestBuilder
diff --git a/tests/MailgunTestCase.php b/tests/MailgunTestCase.php
index 60d835c..ba763c9 100644
--- a/tests/MailgunTestCase.php
+++ b/tests/MailgunTestCase.php
@@ -9,6 +9,8 @@
 
 namespace Mailgun\Tests;
 
-abstract class MailgunTestCase extends \PHPUnit_Framework_TestCase
+use PHPUnit\Framework\TestCase;
+
+abstract class MailgunTestCase extends TestCase
 {
 }
diff --git a/tests/Message/BatchMessageTest.php b/tests/Message/BatchMessageTest.php
index 7c381fa..625cc11 100644
--- a/tests/Message/BatchMessageTest.php
+++ b/tests/Message/BatchMessageTest.php
@@ -13,9 +13,10 @@ use Mailgun\Api\Message;
 use Mailgun\Message\BatchMessage;
 use Mailgun\Message\Exceptions\MissingRequiredParameter;
 use Mailgun\Model\Message\SendResponse;
+use Mailgun\Tests\MailgunTestCase;
 use Nyholm\NSA;
 
-class BatchMessageTest extends \PHPUnit_Framework_TestCase
+class BatchMessageTest extends MailgunTestCase
 {
     /**
      * @var BatchMessage
@@ -146,7 +147,7 @@ class BatchMessageTest extends \PHPUnit_Framework_TestCase
         $this->batchMessage->setSubject('This is the subject of the message!');
         $this->batchMessage->setTextBody('This is the text body of the message!');
 
-        $this->setExpectedException(MissingRequiredParameter::class);
+        $this->expectException(MissingRequiredParameter::class);
         $this->batchMessage->finalize();
     }
 
@@ -155,7 +156,7 @@ class BatchMessageTest extends \PHPUnit_Framework_TestCase
         $this->batchMessage->setFromAddress('samples@mailgun.org', ['first' => 'Test', 'last' => 'User']);
         $this->batchMessage->setSubject('This is the subject of the message!');
         $this->batchMessage->setTextBody('This is the text body of the message!');
-        $this->setExpectedException(MissingRequiredParameter::class);
+        $this->expectException(MissingRequiredParameter::class);
         $this->batchMessage->finalize();
     }
 
@@ -164,7 +165,7 @@ class BatchMessageTest extends \PHPUnit_Framework_TestCase
         $this->batchMessage->addToRecipient('test-user@samples.mailgun.org', ['first' => 'Test', 'last' => 'User']);
         $this->batchMessage->setFromAddress('samples@mailgun.org', ['first' => 'Test', 'last' => 'User']);
         $this->batchMessage->setTextBody('This is the text body of the message!');
-        $this->setExpectedException(MissingRequiredParameter::class);
+        $this->expectException(MissingRequiredParameter::class);
         $this->batchMessage->finalize();
     }
 
@@ -173,7 +174,7 @@ class BatchMessageTest extends \PHPUnit_Framework_TestCase
         $this->batchMessage->addToRecipient('test-user@samples.mailgun.org', ['first' => 'Test', 'last' => 'User']);
         $this->batchMessage->setFromAddress('samples@mailgun.org', ['first' => 'Test', 'last' => 'User']);
         $this->batchMessage->setSubject('This is the subject of the message!');
-        $this->setExpectedException(MissingRequiredParameter::class);
+        $this->expectException(MissingRequiredParameter::class);
         $this->batchMessage->finalize();
     }
 }
diff --git a/tests/Message/MessageBuilderTest.php b/tests/Message/MessageBuilderTest.php
index 3bfee60..6891d50 100644
--- a/tests/Message/MessageBuilderTest.php
+++ b/tests/Message/MessageBuilderTest.php
@@ -10,9 +10,10 @@
 namespace Mailgun\Tests\Message;
 
 use Mailgun\Message\MessageBuilder;
+use Mailgun\Tests\MailgunTestCase;
 use Nyholm\NSA;
 
-class MessageBuilderTest extends \PHPUnit_Framework_TestCase
+class MessageBuilderTest extends MailgunTestCase
 {
     /**
      * @var MessageBuilder
@@ -223,15 +224,10 @@ class MessageBuilderTest extends \PHPUnit_Framework_TestCase
         $this->messageBuilder->setTestMode(true);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:testmode' => 'yes'], $message);
+
         $this->messageBuilder->setTestMode(false);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:testmode' => 'no'], $message);
-        $this->messageBuilder->setTestMode('yes');
-        $message = $this->messageBuilder->getMessage();
-        $this->assertEquals(['o:testmode' => 'yes'], $message);
-        $this->messageBuilder->setTestMode('no');
-        $message = $this->messageBuilder->getMessage();
-        $this->assertEquals(['o:testmode' => 'no'], $message);
     }
 
     public function testAddCampaignId()
@@ -256,15 +252,10 @@ class MessageBuilderTest extends \PHPUnit_Framework_TestCase
         $this->messageBuilder->setDkim(true);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:dkim' => 'yes'], $message);
+
         $this->messageBuilder->setDkim(false);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:dkim' => 'no'], $message);
-        $this->messageBuilder->setDkim('yes');
-        $message = $this->messageBuilder->getMessage();
-        $this->assertEquals(['o:dkim' => 'yes'], $message);
-        $this->messageBuilder->setDkim('no');
-        $message = $this->messageBuilder->getMessage();
-        $this->assertEquals(['o:dkim' => 'no'], $message);
     }
 
     public function testSetClickTracking()
@@ -272,15 +263,18 @@ class MessageBuilderTest extends \PHPUnit_Framework_TestCase
         $this->messageBuilder->setClickTracking(true);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:tracking-clicks' => 'yes'], $message);
+
         $this->messageBuilder->setClickTracking(false);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:tracking-clicks' => 'no'], $message);
-        $this->messageBuilder->setClickTracking('yes');
-        $message = $this->messageBuilder->getMessage();
-        $this->assertEquals(['o:tracking-clicks' => 'yes'], $message);
-        $this->messageBuilder->setClickTracking('no');
+
+        $this->messageBuilder->setClickTracking(false, true);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:tracking-clicks' => 'no'], $message);
+
+        $this->messageBuilder->setClickTracking(true, true);
+        $message = $this->messageBuilder->getMessage();
+        $this->assertEquals(['o:tracking-clicks' => 'htmlonly'], $message);
     }
 
     public function testSetOpenTracking()
@@ -288,15 +282,10 @@ class MessageBuilderTest extends \PHPUnit_Framework_TestCase
         $this->messageBuilder->setOpenTracking(true);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:tracking-opens' => 'yes'], $message);
+
         $this->messageBuilder->setOpenTracking(false);
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:tracking-opens' => 'no'], $message);
-        $this->messageBuilder->setOpenTracking('yes');
-        $message = $this->messageBuilder->getMessage();
-        $this->assertEquals(['o:tracking-opens' => 'yes'], $message);
-        $this->messageBuilder->setOpenTracking('no');
-        $message = $this->messageBuilder->getMessage();
-        $this->assertEquals(['o:tracking-opens' => 'no'], $message);
     }
 
     public function testSetDeliveryTime()
@@ -304,12 +293,15 @@ class MessageBuilderTest extends \PHPUnit_Framework_TestCase
         $this->messageBuilder->setDeliveryTime('January 15, 2014 8:00AM', 'CST');
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:deliverytime' => 'Wed, 15 Jan 2014 08:00:00 -0600'], $message);
+
         $this->messageBuilder->setDeliveryTime('January 15, 2014 8:00AM', 'UTC');
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:deliverytime' => 'Wed, 15 Jan 2014 08:00:00 +0000'], $message);
+
         $this->messageBuilder->setDeliveryTime('January 15, 2014 8:00AM');
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:deliverytime' => 'Wed, 15 Jan 2014 08:00:00 +0000'], $message);
+
         $this->messageBuilder->setDeliveryTime('1/15/2014 13:50:01', 'CDT');
         $message = $this->messageBuilder->getMessage();
         $this->assertEquals(['o:deliverytime' => 'Wed, 15 Jan 2014 13:50:01 -0600'], $message);
diff --git a/tests/Model/BaseModelTest.php b/tests/Model/BaseModelTest.php
index 5b73f0e..562a7e3 100644
--- a/tests/Model/BaseModelTest.php
+++ b/tests/Model/BaseModelTest.php
@@ -9,6 +9,8 @@
 
 namespace Mailgun\Tests\Model;
 
-abstract class BaseModelTest extends \PHPUnit_Framework_TestCase
+use PHPUnit\Framework\TestCase;
+
+abstract class BaseModelTest extends TestCase
 {
 }