diff --git a/.travis.yml b/.travis.yml
index 79178e0..fadbf8c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,6 @@
 language: php
  
 php:
-  - 5.4
   - 5.5
   - 5.6
   - 7.0
diff --git a/README.md b/README.md
index 5468156..51df3bb 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,27 @@ curl -sS https://getcomposer.org/installer | php
 
 # Add Mailgun as a dependency
 php composer.phar require mailgun/mailgun-php:~1.7.2
-``` 
+```
+
+You do also need to choose what library to use when you are sending http messages. Consult the
+[php-http/client-implementation](https://packagist.org/providers/php-http/client-implementation) virtual package to
+find adapters to use. For more information about virtual packages please refer to 
+[Httplug](http://docs.httplug.io/en/latest/virtual-package/). Example:
+
+```bash
+php composer.phar require php-http/guzzle6-adapter:^1.0
+```
+
+When creating a new `Mailgun` object you must provide an instance of the `HttpClient`.
+
+```php
+$client = new \Http\Adapter\Guzzle6\Client();
+$mailgun = new \Mailgun\Mailgun('api_key', $client);
+```
+
+You could also rely on the [auto discovery feature of Httplug](http://docs.php-http.org/en/latest/discovery.html). This 
+means that you need to install `puli/composer-plugin` and put a puli.phar in your project root.  
+
 
 **For shared hosts without SSH access, check out our [Shared Host Instructions](SharedHostInstall.md).**
 
@@ -141,7 +161,9 @@ Go to http://bin.mailgun.net. The Postbin will generate a special URL. Save that
 
 ```php
 # First, instantiate the SDK with your API credentials and define your domain. 
-$mg = new Mailgun('key-example', 'bin.mailgun.net', 'aecf68de', $ssl = False);
+$mg = new Mailgun('key-example', null, 'bin.mailgun.net');
+$mg->setApiVersion('aecf68de');
+$mg->setSslEnabled('false');
 $domain = 'example.com';
 
 # Now, compose and send your message.
diff --git a/composer.json b/composer.json
index 61bc460..6e8618b 100644
--- a/composer.json
+++ b/composer.json
@@ -2,11 +2,15 @@
     "name": "mailgun/mailgun-php",
     "description": "The Mailgun SDK provides methods for all API functions.",
     "require": {
-        "guzzlehttp/guzzle": "~5.0"
+        "php": "^5.5|^7.0",
+        "guzzlehttp/psr7": "~1.2",
+        "php-http/httplug": "^1.0",
+        "php-http/client-implementation": "^1.0",
+        "php-http/discovery": "^0.8"
     },
     "require-dev": {
-        "php": ">=5.4.0",
-        "phpunit/phpunit": "~4.6"
+        "phpunit/phpunit": "~4.6",
+        "php-http/guzzle6-adapter": "^1.0"
     },
     "autoload": {
         "psr-0": {
diff --git a/src/Mailgun/Connection/RestClient.php b/src/Mailgun/Connection/RestClient.php
index 02e65db..1cdc2ee 100644
--- a/src/Mailgun/Connection/RestClient.php
+++ b/src/Mailgun/Connection/RestClient.php
@@ -2,17 +2,17 @@
 
 namespace Mailgun\Connection;
 
-use GuzzleHttp\Client as Guzzle;
-use GuzzleHttp\Message\ResponseInterface;
-use GuzzleHttp\Post\PostBodyInterface;
-use GuzzleHttp\Post\PostFile;
-use GuzzleHttp\Query;
+use GuzzleHttp\Psr7\MultipartStream;
+use GuzzleHttp\Psr7\Request;
+use Http\Client\HttpClient;
+use Http\Discovery\HttpClientDiscovery;
 use Mailgun\Connection\Exceptions\GenericHTTPError;
 use Mailgun\Connection\Exceptions\InvalidCredentials;
 use Mailgun\Connection\Exceptions\MissingRequiredParameters;
 use Mailgun\Connection\Exceptions\MissingEndpoint;
 use Mailgun\Constants\Api;
 use Mailgun\Constants\ExceptionMessages;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * This class is a wrapper for the Guzzle (HTTP Client Library).
@@ -20,35 +20,73 @@ use Mailgun\Constants\ExceptionMessages;
 class RestClient
 {
     /**
+     * Your API key
      * @var string
      */
     private $apiKey;
 
     /**
-     * @var Guzzle
+     * @var HttpClient
      */
-    protected $mgClient;
+    protected $httpClient;
 
     /**
-     * @param string $apiKey
-     * @param string $apiEndpoint
-     * @param string $apiVersion
-     * @param bool   $ssl
+     * @var string
      */
-    public function __construct($apiKey, $apiEndpoint, $apiVersion, $ssl)
+    protected $apiHost;
+
+    /**
+     * The version of the API to use
+     * @var string
+     */
+    protected $apiVersion = 'v2';
+
+    /**
+     * If we should use SSL or not
+     * @var bool
+     */
+    protected $sslEnabled = true;
+
+    /**
+     * @param string      $apiKey
+     * @param string      $apiHost
+     * @param HttpClient  $httpClient
+     */
+    public function __construct($apiKey, $apiHost, HttpClient $httpClient = null)
     {
         $this->apiKey = $apiKey;
-        $this->mgClient = new Guzzle([
-            'base_url'=>$this->generateEndpoint($apiEndpoint, $apiVersion, $ssl),
-            'defaults'=>[
-                'auth' => array(Api::API_USER, $this->apiKey),
-                'exceptions' => false,
-                'config' => ['curl' => [ CURLOPT_FORBID_REUSE => true ]],
-                'headers' => [
-                    'User-Agent' => Api::SDK_USER_AGENT.'/'.Api::SDK_VERSION,
-                ],
-            ],
-        ]);
+        $this->apiHost = $apiHost;
+        $this->httpClient = $httpClient;
+    }
+
+    /**
+     * @param string $method
+     * @param string $uri
+     * @param array  $body
+     * @param array  $files
+     * @param array  $headers
+     *
+     * @return \stdClass
+     *
+     * @throws GenericHTTPError
+     * @throws InvalidCredentials
+     * @throws MissingEndpoint
+     * @throws MissingRequiredParameters
+     */
+    protected function send($method, $uri, $body = null, $files = [], array $headers = [])
+    {
+        $headers['User-Agent'] = Api::SDK_USER_AGENT.'/'.Api::SDK_VERSION;
+        $headers['Authorization'] = 'Basic '.base64_encode(sprintf('%s:%s', Api::API_USER, $this->apiKey));
+
+        if (!empty($files)) {
+            $body = new MultipartStream($files);
+            $headers['Content-Type'] = 'multipart/form-data; boundary='.$body->getBoundary();
+        }
+
+        $request = new Request($method, $this->getApiUrl($uri), $headers, $body);
+        $response = $this->getHttpClient()->sendRequest($request);
+
+        return $this->responseHandler($response);
     }
 
     /**
@@ -65,27 +103,39 @@ class RestClient
      */
     public function post($endpointUrl, $postData = array(), $files = array())
     {
-        $request = $this->mgClient->createRequest('POST', $endpointUrl, ['body' => $postData]);
-        /** @var \GuzzleHttp\Post\PostBodyInterface $postBody */
-        $postBody = $request->getBody();
-        $postBody->setAggregator(Query::duplicateAggregator());
+        $postFiles = [];
 
         $fields = ['message', 'attachment', 'inline'];
         foreach ($fields as $fieldName) {
             if (isset($files[$fieldName])) {
                 if (is_array($files[$fieldName])) {
                     foreach ($files[$fieldName] as $file) {
-                        $this->addFile($postBody, $fieldName, $file);
+                        $postFiles[] = $this->prepareFile($fieldName, $file);
                     }
                 } else {
-                    $this->addFile($postBody, $fieldName, $files[$fieldName]);
+                    $postFiles[] = $this->prepareFile($fieldName, $files[$fieldName]);
                 }
             }
         }
 
-        $response = $this->mgClient->send($request);
+        $postDataMultipart = [];
+        foreach ($postData as $key => $value) {
+            if (is_array($value)) {
+                foreach ($value as $subValue) {
+                    $postDataMultipart[] = [
+                        'name' => $key,
+                        'contents' => $subValue,
+                    ];
+                }
+            } else {
+                $postDataMultipart[] = [
+                    'name' => $key,
+                    'contents' => $value,
+                ];
+            }
+        }
 
-        return $this->responseHandler($response);
+        return $this->send('POST', $endpointUrl, [], array_merge($postDataMultipart, $postFiles));
     }
 
     /**
@@ -101,9 +151,7 @@ class RestClient
      */
     public function get($endpointUrl, $queryString = array())
     {
-        $response = $this->mgClient->get($endpointUrl, ['query' => $queryString]);
-
-        return $this->responseHandler($response);
+        return $this->send('GET', $endpointUrl.'?'.http_build_query($queryString));
     }
 
     /**
@@ -118,9 +166,7 @@ class RestClient
      */
     public function delete($endpointUrl)
     {
-        $response = $this->mgClient->delete($endpointUrl);
-
-        return $this->responseHandler($response);
+        return $this->send('DELETE', $endpointUrl);
     }
 
     /**
@@ -136,14 +182,7 @@ class RestClient
      */
     public function put($endpointUrl, $putData)
     {
-        $request = $this->mgClient->createRequest('PUT', $endpointUrl, ['body' => $putData]);
-        /** @var \GuzzleHttp\Post\PostBodyInterface $postBody */
-        $postBody = $request->getBody();
-        $postBody->setAggregator(Query::duplicateAggregator());
-
-        $response = $this->mgClient->send($request);
-
-        return $this->responseHandler($response);
+        return $this->send('PUT', $endpointUrl, $putData);
     }
 
     /**
@@ -156,7 +195,7 @@ class RestClient
      * @throws MissingEndpoint
      * @throws MissingRequiredParameters
      */
-    public function responseHandler($responseObj)
+    public function responseHandler(ResponseInterface $responseObj)
     {
         $httpResponseCode = $responseObj->getStatusCode();
         if ($httpResponseCode === 200) {
@@ -180,43 +219,26 @@ class RestClient
     }
 
     /**
-     * @param \Guzzle\Http\Message\Response $responseObj
+     * @param ResponseInterface $responseObj
      *
      * @return string
      */
-    protected function getResponseExceptionMessage(\GuzzleHttp\Message\Response $responseObj)
+    protected function getResponseExceptionMessage(ResponseInterface $responseObj)
     {
         $body = (string) $responseObj->getBody();
         $response = json_decode($body);
         if (json_last_error() == JSON_ERROR_NONE && isset($response->message)) {
-            return " ".$response->message;
+            return ' '.$response->message;
         }
     }
 
     /**
-     * @param string $apiEndpoint
-     * @param string $apiVersion
-     * @param bool   $ssl
+     * Prepare a file for the postBody.
      *
-     * @return string
+     * @param string       $fieldName
+     * @param string|array $filePath
      */
-    private function generateEndpoint($apiEndpoint, $apiVersion, $ssl)
-    {
-        if (!$ssl) {
-            return "http://".$apiEndpoint."/".$apiVersion."/";
-        } else {
-            return "https://".$apiEndpoint."/".$apiVersion."/";
-        }
-    }
-
-    /**
-     * Add a file to the postBody.
-     *
-     * @param PostBodyInterface $postBody
-     * @param string            $fieldName
-     * @param string|array      $filePath
-     */
-    private function addFile(PostBodyInterface $postBody, $fieldName, $filePath)
+    protected function prepareFile($fieldName, $filePath)
     {
         $filename = null;
         // Backward compatibility code
@@ -230,6 +252,75 @@ class RestClient
             $filePath = substr($filePath, 1);
         }
 
-        $postBody->addFile(new PostFile($fieldName, fopen($filePath, 'r'), $filename));
+        return [
+            'name' => $fieldName,
+            'contents' => fopen($filePath, 'r'),
+            'filename' => $filename,
+        ];
+    }
+
+
+    /**
+     *
+     * @return HttpClient
+     */
+    protected function getHttpClient()
+    {
+        if ($this->httpClient === null) {
+            $this->httpClient = HttpClientDiscovery::find();
+        }
+
+        return $this->httpClient;
+    }
+
+    /**
+     * @param $uri
+     *
+     * @return string
+     */
+    private function getApiUrl($uri)
+    {
+        return $this->generateEndpoint($this->apiHost, $this->apiVersion, $this->sslEnabled).$uri;
+    }
+
+
+    /**
+     * @param string $apiEndpoint
+     * @param string $apiVersion
+     * @param bool   $ssl
+     *
+     * @return string
+     */
+    private function generateEndpoint($apiEndpoint, $apiVersion, $ssl)
+    {
+        if (!$ssl) {
+            return 'http://'.$apiEndpoint.'/'.$apiVersion.'/';
+        } else {
+            return 'https://'.$apiEndpoint.'/'.$apiVersion.'/';
+        }
+    }
+
+    /**
+     * @param string $apiVersion
+     *
+     * @return RestClient
+     */
+    public function setApiVersion($apiVersion)
+    {
+        $this->apiVersion = $apiVersion;
+
+        return $this;
+    }
+
+    /**
+     * @param boolean $sslEnabled
+     *
+     * @return RestClient
+     */
+    public function setSslEnabled($sslEnabled)
+    {
+        $this->sslEnabled = $sslEnabled;
+
+        return $this;
     }
 }
diff --git a/src/Mailgun/Mailgun.php b/src/Mailgun/Mailgun.php
index f9921ef..6777801 100644
--- a/src/Mailgun/Mailgun.php
+++ b/src/Mailgun/Mailgun.php
@@ -2,6 +2,7 @@
 
 namespace Mailgun;
 
+use Http\Client\HttpClient;
 use Mailgun\Constants\ExceptionMessages;
 use Mailgun\Messages\Exceptions;
 use Mailgun\Connection\RestClient;
@@ -29,13 +30,16 @@ class Mailgun{
 
     /**
      * @param string|null $apiKey
+     * @param HttpClient $httpClient
      * @param string $apiEndpoint
-     * @param string $apiVersion
-     * @param bool $ssl
      */
-    public function __construct($apiKey = null, $apiEndpoint = "api.mailgun.net", $apiVersion = "v3", $ssl = true){
+    public function __construct(
+        $apiKey = null,
+        HttpClient $httpClient = null,
+        $apiEndpoint = 'api.mailgun.net'
+    ) {
         $this->apiKey = $apiKey;
-        $this->restClient = new RestClient($apiKey, $apiEndpoint, $apiVersion, $ssl);
+        $this->restClient = new RestClient($apiKey, $apiEndpoint, $httpClient);
     }
 
     /**
@@ -132,6 +136,30 @@ class Mailgun{
         return $this->restClient->put($endpointUrl, $putData);
     }
 
+    /**
+     * @param string $apiVersion
+     *
+     * @return Mailgun
+     */
+    public function setApiVersion($apiVersion)
+    {
+        $this->restClient->setApiVersion($apiVersion);
+
+        return $this;
+    }
+
+    /**
+     * @param boolean $sslEnabled
+     *
+     * @return Mailgun
+     */
+    public function setSslEnabled($sslEnabled)
+    {
+        $this->restClient->setSslEnabled($sslEnabled);
+
+        return $this;
+    }
+
     /**
      * @return MessageBuilder
      */
diff --git a/tests/Mailgun/Tests/Connection/ConnectionTest.php b/tests/Mailgun/Tests/Connection/ConnectionTest.php
deleted file mode 100644
index aed26de..0000000
--- a/tests/Mailgun/Tests/Connection/ConnectionTest.php
+++ /dev/null
@@ -1,19 +0,0 @@
-<?PHP
-namespace Mailgun\Tests\Connection;
-
-use Mailgun\Tests\Mock\Mailgun;
-
-class ConnectionTest extends \Mailgun\Tests\MailgunTestCase
-{
-
-    private $client;
-
-    public function setUp()
-    {
-    }
-
-    public function testNewClientInstantiation()
-    {
-        $this->client = new Mailgun("My-Super-Awesome-API-Key", "samples.mailgun.org", false);
-    }
-}
diff --git a/tests/Mailgun/Tests/Messages/MessageBuilderTest.php b/tests/Mailgun/Tests/Messages/MessageBuilderTest.php
index 4a46eea..8daf2e3 100644
--- a/tests/Mailgun/Tests/Messages/MessageBuilderTest.php
+++ b/tests/Mailgun/Tests/Messages/MessageBuilderTest.php
@@ -9,7 +9,7 @@ class MessageBuilderTest extends \Mailgun\Tests\MailgunTestCase
 
     public function setUp()
     {
-        $this->client = new Mailgun("My-Super-Awesome-API-Key", "samples.mailgun.org", false);
+        $this->client = new Mailgun();
     }
 
     public function testBlankInstantiation()
diff --git a/tests/Mailgun/Tests/Mock/Connection/TestBroker.php b/tests/Mailgun/Tests/Mock/Connection/TestBroker.php
index a9ee3b0..6652aa5 100644
--- a/tests/Mailgun/Tests/Mock/Connection/TestBroker.php
+++ b/tests/Mailgun/Tests/Mock/Connection/TestBroker.php
@@ -13,10 +13,10 @@ class TestBroker extends RestClient
 
     protected $apiEndpoint;
 
-    public function __construct($apiKey = null, $apiEndpoint = "api.mailgun.net", $apiVersion = "v3")
+    public function __construct($apiKey = null, $apiHost = "api.mailgun.net", $apiVersion = "v3")
     {
         $this->apiKey      = $apiKey;
-        $this->apiEndpoint = $apiEndpoint;
+        $this->apiEndpoint = $apiHost;
     }
 
     public function post($endpointUrl, $postData = array(), $files = array())