diff --git a/.travis.yml b/.travis.yml
index cf5da1d..79178e0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,16 +1,17 @@
 language: php
  
 php:
-  - 5.3
   - 5.4
   - 5.5
   - 5.6
+  - 7.0
   - hhvm
 
-matrix:
-  allow_failures:
-    - php: hhvm
+before_install:
+  - travis_retry composer self-update
 
-before_script:
-  - echo 'Installing composer dependencies now!'
-  - composer install
+install:
+  - travis_retry composer install
+
+script:
+  - phpunit
\ No newline at end of file
diff --git a/composer.json b/composer.json
index 1a9baa7..61bc460 100644
--- a/composer.json
+++ b/composer.json
@@ -2,10 +2,11 @@
     "name": "mailgun/mailgun-php",
     "description": "The Mailgun SDK provides methods for all API functions.",
     "require": {
-        "guzzle/guzzle": "<4.0,>=3.8"
+        "guzzlehttp/guzzle": "~5.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "3.7.*"
+        "php": ">=5.4.0",
+        "phpunit/phpunit": "~4.6"
     },
     "autoload": {
         "psr-0": {
diff --git a/src/Mailgun/Connection/RestClient.php b/src/Mailgun/Connection/RestClient.php
index 12b7c56..e78b39f 100644
--- a/src/Mailgun/Connection/RestClient.php
+++ b/src/Mailgun/Connection/RestClient.php
@@ -2,11 +2,12 @@
 
 namespace Mailgun\Connection;
 
-use Guzzle\Http\Client as Guzzle;
-
+use GuzzleHttp\Client as Guzzle;
+use GuzzleHttp\Message\ResponseInterface;
+use GuzzleHttp\Post\PostBodyInterface;
+use GuzzleHttp\Post\PostFile;
+use GuzzleHttp\Query;
 use Mailgun\Connection\Exceptions\GenericHTTPError;
-use Guzzle\Http\QueryAggregator\DuplicateAggregator;
-use Guzzle\Http\QueryAggregator\PhpAggregator;
 use Mailgun\Connection\Exceptions\InvalidCredentials;
 use Mailgun\Connection\Exceptions\MissingRequiredParameters;
 use Mailgun\Connection\Exceptions\MissingEndpoint;
@@ -16,213 +17,219 @@ use Mailgun\Constants\ExceptionMessages;
 /**
  * This class is a wrapper for the Guzzle (HTTP Client Library).
  */
-class RestClient {
-
+class RestClient
+{
     /**
      * @var string
      */
-	private $apiKey;
+    private $apiKey;
 
     /**
      * @var Guzzle
      */
-	protected $mgClient;
-
-    /**
-     * @var bool
-     */
-	protected $hasFiles = False;
+    protected $mgClient;
 
     /**
      * @param string $apiKey
      * @param string $apiEndpoint
      * @param string $apiVersion
-     * @param bool $ssl
+     * @param bool   $ssl
      */
-	public function __construct($apiKey, $apiEndpoint, $apiVersion, $ssl){
-		$this->apiKey = $apiKey;
-		$this->mgClient = new Guzzle($this->generateEndpoint($apiEndpoint, $apiVersion, $ssl));
-		$this->mgClient->setDefaultOption('curl.options', array('CURLOPT_FORBID_REUSE' => true));
-		$this->mgClient->setDefaultOption('auth', array (Api::API_USER, $this->apiKey));
-		$this->mgClient->setDefaultOption('exceptions', false);
-		$this->mgClient->setUserAgent(Api::SDK_USER_AGENT . '/' . Api::SDK_VERSION);
-	}
+    public function __construct($apiKey, $apiEndpoint, $apiVersion, $ssl)
+    {
+        $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,
+                ],
+            ],
+        ]);
+    }
 
     /**
      * @param string $endpointUrl
-     * @param array $postData
-     * @param array $files
+     * @param array  $postData
+     * @param array  $files
+     *
      * @return \stdClass
+     *
      * @throws GenericHTTPError
      * @throws InvalidCredentials
      * @throws MissingEndpoint
      * @throws MissingRequiredParameters
      */
-	public function post($endpointUrl, $postData = array(), $files = array()){
-		$request = $this->mgClient->post($endpointUrl, array(), $postData);
+    public function post($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());
 
-		if(isset($files["message"])){
-			$this->hasFiles = True;
-			foreach($files as $message){
-				$request->addPostFile("message", $message);
-			}
-		}
+        $fields = ['message', 'attachment', 'inline'];
+        foreach ($fields as $fieldName) {
+            if (isset($files[$fieldName])) {
+                if (is_array($files[$fieldName])) {
+                    foreach ($files[$fieldName] as $file) {
+                        $this->addFile($postBody, $fieldName, $file);
+                    }
+                } else {
+                    $this->addFile($postBody, $fieldName, $files[$fieldName]);
+                }
+            }
+        }
 
-		if(isset($files["attachment"])){
-			$this->hasFiles = True;
-			foreach($files["attachment"] as $attachment){
-				// Backward compatibility code
-				if (is_array($attachment)){
-					$request->addPostFile("attachment",
-										  $attachment['filePath'], null,
-										  $attachment['remoteName']);
-				}
-				else{
-					$request->addPostFile("attachment", $attachment);
-				}
-			}
-		}
+        $response = $this->mgClient->send($request);
 
-		if(isset($files["inline"])){
-			$this->hasFiles = True;
-			foreach($files["inline"] as $inline){
-				// Backward compatibility code
-				if (is_array($inline)){
-					$request->addPostFile("inline",
-										  $inline['filePath'], null,
-										  $inline['remoteName']);
-				}
-				else{
-					$request->addPostFile("inline", $inline);
-				}
-			}
-		}
-
-		/*
-			This block of code is to accommodate for a bug in Guzzle.
-			See https://github.com/guzzle/guzzle/issues/545.
-			It can be removed when Guzzle resolves the issue.
-		*/
-
-		if($this->hasFiles){
-			$request->getPostFields()->setAggregator(new PhpAggregator());
-		}
-
-		else{
-			$request->getPostFields()->setAggregator(new DuplicateAggregator());
-		}
-
-		$response = $request->send();
-		return $this->responseHandler($response);
-	}
+        return $this->responseHandler($response);
+    }
 
     /**
      * @param string $endpointUrl
-     * @param array $queryString
+     * @param array  $queryString
+     *
      * @return \stdClass
+     *
      * @throws GenericHTTPError
      * @throws InvalidCredentials
      * @throws MissingEndpoint
      * @throws MissingRequiredParameters
      */
-	public function get($endpointUrl, $queryString = array()){
-		$request = $this->mgClient->get($endpointUrl);
-		if(isset($queryString)){
-			foreach($queryString as $key=>$value){
-				$request->getQuery()->set($key, $value);
-			}
-		}
-		$response = $request->send();
-		return $this->responseHandler($response);
-	}
+    public function get($endpointUrl, $queryString = array())
+    {
+        $response = $this->mgClient->get($endpointUrl, ['query' => $queryString]);
+
+        return $this->responseHandler($response);
+    }
 
     /**
      * @param string $endpointUrl
+     *
      * @return \stdClass
+     *
      * @throws GenericHTTPError
      * @throws InvalidCredentials
      * @throws MissingEndpoint
      * @throws MissingRequiredParameters
      */
-	public function delete($endpointUrl){
-		$request = $this->mgClient->delete($endpointUrl);
-		$response = $request->send();
-		return $this->responseHandler($response);
-	}
+    public function delete($endpointUrl)
+    {
+        $response = $this->mgClient->delete($endpointUrl);
+
+        return $this->responseHandler($response);
+    }
 
     /**
      * @param string $endpointUrl
-     * @param array $putData
+     * @param array  $putData
+     *
      * @return \stdClass
+     *
      * @throws GenericHTTPError
      * @throws InvalidCredentials
      * @throws MissingEndpoint
      * @throws MissingRequiredParameters
      */
-	public function put($endpointUrl, $putData){
-		$request = $this->mgClient->put($endpointUrl, array(), $putData);
-		$request->getPostFields()->setAggregator(new DuplicateAggregator());
-		$response = $request->send();
-		return $this->responseHandler($response);
-	}
-
-    /**
-     * @param \Guzzle\Http\Message\Response $responseObj
-     * @return \stdClass
-     * @throws GenericHTTPError
-     * @throws InvalidCredentials
-     * @throws MissingEndpoint
-     * @throws MissingRequiredParameters
-     */
-	public function responseHandler($responseObj){
-		$httpResponseCode = $responseObj->getStatusCode();
-		if($httpResponseCode === 200){
-			$data = (string) $responseObj->getBody();
-			$jsonResponseData = json_decode($data, false);
-			$result = new \stdClass();
-			// return response data as json if possible, raw if not
-			$result->http_response_body = $data && $jsonResponseData === null ? $data : $jsonResponseData;
-		}
-		elseif($httpResponseCode == 400){
-			throw new MissingRequiredParameters(ExceptionMessages::EXCEPTION_MISSING_REQUIRED_PARAMETERS . $this->getResponseExceptionMessage($responseObj));
-		}
-		elseif($httpResponseCode == 401){
-			throw new InvalidCredentials(ExceptionMessages::EXCEPTION_INVALID_CREDENTIALS);
-		}
-		elseif($httpResponseCode == 404){
-			throw new MissingEndpoint(ExceptionMessages::EXCEPTION_MISSING_ENDPOINT  . $this->getResponseExceptionMessage($responseObj));
-		}
-		else{
-			throw new GenericHTTPError(ExceptionMessages::EXCEPTION_GENERIC_HTTP_ERROR, $httpResponseCode, $responseObj->getBody());
-		}
-		$result->http_response_code = $httpResponseCode;
-		return $result;
-	}
+    public function put($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);
+    }
+
+    /**
+     * @param ResponseInterface $responseObj
+     *
+     * @return \stdClass
+     *
+     * @throws GenericHTTPError
+     * @throws InvalidCredentials
+     * @throws MissingEndpoint
+     * @throws MissingRequiredParameters
+     */
+    public function responseHandler($responseObj)
+    {
+        $httpResponseCode = $responseObj->getStatusCode();
+        if ($httpResponseCode === 200) {
+            $data = (string) $responseObj->getBody();
+            $jsonResponseData = json_decode($data, false);
+            $result = new \stdClass();
+            // return response data as json if possible, raw if not
+            $result->http_response_body = $data && $jsonResponseData === null ? $data : $jsonResponseData;
+        } elseif ($httpResponseCode == 400) {
+            throw new MissingRequiredParameters(ExceptionMessages::EXCEPTION_MISSING_REQUIRED_PARAMETERS.$this->getResponseExceptionMessage($responseObj));
+        } elseif ($httpResponseCode == 401) {
+            throw new InvalidCredentials(ExceptionMessages::EXCEPTION_INVALID_CREDENTIALS);
+        } elseif ($httpResponseCode == 404) {
+            throw new MissingEndpoint(ExceptionMessages::EXCEPTION_MISSING_ENDPOINT.$this->getResponseExceptionMessage($responseObj));
+        } else {
+            throw new GenericHTTPError(ExceptionMessages::EXCEPTION_GENERIC_HTTP_ERROR, $httpResponseCode, $responseObj->getBody());
+        }
+        $result->http_response_code = $httpResponseCode;
+
+        return $result;
+    }
 
     /**
      * @param \Guzzle\Http\Message\Response $responseObj
+     *
      * @return string
      */
-	protected function getResponseExceptionMessage(\Guzzle\Http\Message\Response $responseObj){
-		$body = (string)$responseObj->getBody();
-		$response = json_decode($body);
-		if (json_last_error() == JSON_ERROR_NONE && isset($response->message)) {
-			return " " . $response->message;
-		}
-	}
+    protected function getResponseExceptionMessage(\Guzzle\Http\Message\Response $responseObj)
+    {
+        $body = (string) $responseObj->getBody();
+        $response = json_decode($body);
+        if (json_last_error() == JSON_ERROR_NONE && isset($response->message)) {
+            return " ".$response->message;
+        }
+    }
 
     /**
      * @param string $apiEndpoint
      * @param string $apiVersion
-     * @param bool $ssl
+     * @param bool   $ssl
+     *
      * @return string
      */
-	private function generateEndpoint($apiEndpoint, $apiVersion, $ssl){
-		if(!$ssl){
-			return "http://" . $apiEndpoint . "/" . $apiVersion . "/";
-		}
-		else{
-			return "https://" . $apiEndpoint . "/" . $apiVersion . "/";
-		}
-	}
+    private function generateEndpoint($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)
+    {
+        $filename = null;
+        // Backward compatibility code
+        if (is_array($filePath)) {
+            $filename = $filePath['remoteName'];
+            $filePath = $filePath['filePath'];
+        }
+
+        // Remove leading @ symbol
+        if (strpos($filePath, '@') === 0) {
+            $filePath = substr($filePath, 1);
+        }
+
+        $postBody->addFile(new PostFile($fieldName, fopen($filePath, 'r'), $filename));
+    }
 }
diff --git a/tests/Mailgun/Tests/MailgunTestCase.php b/tests/Mailgun/Tests/MailgunTestCase.php
index 0f476e8..3d8f2e6 100644
--- a/tests/Mailgun/Tests/MailgunTestCase.php
+++ b/tests/Mailgun/Tests/MailgunTestCase.php
@@ -2,8 +2,6 @@
 
 namespace Mailgun\Tests;
 
-use Guzzle\Tests\GuzzleTestCase;
-
-abstract class MailgunTestCase extends GuzzleTestCase
+abstract class MailgunTestCase extends \PHPUnit_Framework_TestCase
 {
 }
diff --git a/tests/Mailgun/Tests/Mock/Connection/TestBroker.php b/tests/Mailgun/Tests/Mock/Connection/TestBroker.php
index 23baeb9..a9ee3b0 100644
--- a/tests/Mailgun/Tests/Mock/Connection/TestBroker.php
+++ b/tests/Mailgun/Tests/Mock/Connection/TestBroker.php
@@ -1,7 +1,11 @@
 <?php
 namespace Mailgun\Tests\Mock\Connection;
 
+use Mailgun\Connection\Exceptions\GenericHTTPError;
+use Mailgun\Connection\Exceptions\InvalidCredentials;
+use Mailgun\Connection\Exceptions\MissingEndpoint;
 use Mailgun\Connection\RestClient;
+use Mailgun\Messages\Exceptions\MissingRequiredMIMEParameters;
 
 class TestBroker extends RestClient
 {
@@ -17,25 +21,25 @@ class TestBroker extends RestClient
 
     public function post($endpointUrl, $postData = array(), $files = array())
     {
-        return $this->responseHandler($endpointUrl, $httpResponseCode = 200);
+        return $this->testResponseHandler($endpointUrl, $httpResponseCode = 200);
     }
 
     public function get($endpointUrl, $queryString = array())
     {
-        return $this->responseHandler($endpointUrl, $httpResponseCode = 200);
+        return $this->testResponseHandler($endpointUrl, $httpResponseCode = 200);
     }
 
     public function delete($endpointUrl)
     {
-        return $this->responseHandler($endpointUrl, $httpResponseCode = 200);
+        return $this->testResponseHandler($endpointUrl, $httpResponseCode = 200);
     }
 
     public function put($endpointUrl, $queryString)
     {
-        return $this->responseHandler($endpointUrl, $httpResponseCode = 200);
+        return $this->testResponseHandler($endpointUrl, $httpResponseCode = 200);
     }
 
-    public function responseHandler($endpointUrl, $httpResponseCode = 200)
+    public function testResponseHandler($endpointUrl, $httpResponseCode = 200)
     {
         if ($httpResponseCode === 200) {
             $result                     = new \stdClass();
@@ -44,13 +48,13 @@ class TestBroker extends RestClient
             foreach ($jsonResponseData as $key => $value) {
                 $result->http_response_body->$key = $value;
             }
-        } elseif ($httpStatusCode == 400) {
+        } elseif ($httpResponseCode == 400) {
             throw new MissingRequiredMIMEParameters(EXCEPTION_MISSING_REQUIRED_MIME_PARAMETERS);
-        } elseif ($httpStatusCode == 401) {
+        } elseif ($httpResponseCode == 401) {
             throw new InvalidCredentials(EXCEPTION_INVALID_CREDENTIALS);
-        } elseif ($httpStatusCode == 401) {
+        } elseif ($httpResponseCode == 401) {
             throw new GenericHTTPError(EXCEPTION_INVALID_CREDENTIALS);
-        } elseif ($httpStatusCode == 404) {
+        } elseif ($httpResponseCode == 404) {
             throw new MissingEndpoint(EXCEPTION_MISSING_ENDPOINT);
         } else {
             throw new GenericHTTPError(EXCEPTION_GENERIC_HTTP_ERROR);