diff --git a/.travis.yml b/.travis.yml
index 2f3f780..aa3aaac 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -31,7 +31,7 @@ before_script:
 
 script:
   - sh -c "if [ '$DEFAULT' = '1' ]; then composer test; fi"
-  - sh -c "if [ '$PHPSTAN' = '1' ]; then composer require --dev "phpstan/phpstan:^0.10" && composer phpstan; fi"
+  - sh -c "if [ '$PHPSTAN' = '1' ]; then composer require --dev "phpstan/phpstan:^0.12" && composer phpstan; fi"
   - sh -c "if [ '$PHPCS' = '1' ]; then composer cs-check; fi"
   - sh -c "if [ '$CODECOVERAGE' = '1' ]; then phpdbg -qrr vendor/bin/phpunit --coverage-clover=clover.xml || true; fi"
 
diff --git a/composer.json b/composer.json
index 23a3430..05d11f5 100644
--- a/composer.json
+++ b/composer.json
@@ -44,7 +44,7 @@
         ],
         "cs-check": "phpcs --colors -p --standard=vendor/cakephp/cakephp-codesniffer/CakePHP src/ tests/",
         "cs-fix": "phpcbf --colors --standard=vendor/cakephp/cakephp-codesniffer/CakePHP src/ tests/",
-        "phpstan": "phpstan analyze -l 1 src/",
+        "phpstan": "phpstan analyze src/",
         "test": "phpunit --colors=always"
     }
 }
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..d39df6a
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,8 @@
+parameters:
+    level: 7
+    checkMissingIterableValueType: false
+    autoload_files:
+        - tests/bootstrap.php
+    ignoreErrors:
+            - '#Parameter \#1 \$str of function trim expects string, array\|string given.#'
+            - '#Result of \|\| is always true.#'
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index cf3edac..e9f2bb2 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -9,6 +9,9 @@
     <php>
         <ini name="memory_limit" value="-1"/>
         <ini name="apc.enable_cli" value="1"/>
+        <!-- E_ALL => 32767 -->
+        <!-- E_ALL & ~E_USER_DEPRECATED => 16383 -->
+        <ini name="error_reporting" value="16383"/>
     </php>
 
     <!-- Add any additional test suites you want to run here -->
diff --git a/src/Mailer/Transport/MailgunTransport.php b/src/Mailer/Transport/MailgunTransport.php
index 41333b6..7a0eac6 100644
--- a/src/Mailer/Transport/MailgunTransport.php
+++ b/src/Mailer/Transport/MailgunTransport.php
@@ -37,7 +37,7 @@ class MailgunTransport extends AbstractTransport
     protected $_defaultConfig = [
         'apiEndpoint' => 'https://api.mailgun.net/v3',
         'domain' => '',
-        'apiKey' => ''
+        'apiKey' => '',
     ];
 
     /**
@@ -54,7 +54,7 @@ class MailgunTransport extends AbstractTransport
         'tracking-clicks',
         'tracking-opens',
         'require-tls',
-        'skip-verification'
+        'skip-verification',
     ];
 
     /**
@@ -135,9 +135,9 @@ public function send(Email $email)
         if (!empty($attachments)) {
             foreach ($attachments as $fileName => $attachment) {
                 if (empty($attachment['contentId'])) {
-                    $file = $this->_addFile('attachment', $attachment, $fileName);
+                    $file = $this->_addFile('attachment', $attachment, (string)$fileName);
                 } else {
-                    $file = $this->_addFile('inline', $attachment, $fileName);
+                    $file = $this->_addFile('inline', $attachment, (string)$fileName);
                     $file->contentId($attachment['contentId']);
                 }
                 $file->disposition('attachment');
@@ -181,7 +181,7 @@ protected function _addFile($partName, $attachment, $fileName = '')
     /**
      * Returns the parameters for API request.
      *
-     * @return array
+     * @return \Cake\Http\Client\FormData
      */
     public function getRequestData()
     {
@@ -344,6 +344,10 @@ protected function _prepareEmailAddresses(Email $email)
         foreach ($email->getBcc() as $bccEmail => $bccName) {
             $this->_formData->add('bcc', sprintf("%s <%s>", $bccName, $bccEmail));
         }
+
+        foreach ($email->getReplyTo() as $replyToEmail => $replyToName) {
+            $this->_formData->add('h:Reply-To', sprintf("%s <%s>", $replyToName, $replyToEmail));
+        }
     }
 
     /**
@@ -356,7 +360,7 @@ protected function _sendEmail()
         $http = new Client();
         $response = $http->post("{$this->getConfig('apiEndpoint')}/{$this->getConfig('domain')}/messages", (string)$this->_formData, [
             'auth' => ['username' => 'api', 'password' => $this->getConfig('apiKey')],
-            'headers' => ['Content-Type' => $this->_formData->contentType()]
+            'headers' => ['Content-Type' => $this->_formData->contentType()],
         ]);
 
         return $response->getJson();
diff --git a/tests/TestCase/Mailer/Transport/MailgunTransportTest.php b/tests/TestCase/Mailer/Transport/MailgunTransportTest.php
index b527dc9..5b49a4f 100644
--- a/tests/TestCase/Mailer/Transport/MailgunTransportTest.php
+++ b/tests/TestCase/Mailer/Transport/MailgunTransportTest.php
@@ -85,6 +85,7 @@ public function testAdditionalEmailAddresses()
             ->setTo('to@example.com')
             ->addCC(['ccbar@example.com', 'ccjohn@example.com' => 'John'])
             ->addBcc(['bccbar@example.com', 'bccjohn@example.com' => 'John'])
+            ->setReplyTo(['replyto@example.com' => 'John'])
             ->setEmailFormat('both')
             ->setSubject('Email from CakePHP Mailgun plugin')
             ->send('Hello there, <br> This is an email from CakePHP Mailgun Email plugin.');
@@ -99,12 +100,35 @@ public function testAdditionalEmailAddresses()
         $this->assertTextContains('Content-Disposition: form-data; name="to"', $reqDataString);
         $this->assertTextContains('Content-Disposition: form-data; name="cc"', $reqDataString);
         $this->assertTextContains('Content-Disposition: form-data; name="bcc"', $reqDataString);
+        $this->assertTextContains('Content-Disposition: form-data; name="h:Reply-To"', $reqDataString);
         $this->assertTextContains('from@example.com <from@example.com>', $reqDataString);
         $this->assertTextContains('to@example.com <to@example.com>', $reqDataString);
         $this->assertTextContains('ccbar@example.com <ccbar@example.com>', $reqDataString);
         $this->assertTextContains('John <ccjohn@example.com>', $reqDataString);
         $this->assertTextContains('bccbar@example.com <bccbar@example.com>', $reqDataString);
         $this->assertTextContains('John <bccjohn@example.com>', $reqDataString);
+        $this->assertTextContains('John <replyto@example.com>', $reqDataString);
+    }
+
+    public function testCustomHeaders()
+    {
+        $this->_setEmailConfig();
+        $email = new Email();
+        $email->setProfile(['transport' => 'mailgun']);
+        $res = $email->setFrom('from@example.com')
+            ->setTo('to@example.com')
+            ->setHeaders(['h:X-MyHeader' => 'YouGotIt'])
+            ->setSubject('Email from CakePHP Mailgun plugin')
+            ->send('Hello there, <br> This is an email from CakePHP Mailgun Email plugin.');
+
+        $reqData = $res['reqData'];
+        $boundary = $reqData->boundary();
+        $reqDataString = (string)$reqData;
+
+        $this->assertNotEmpty($reqDataString);
+        $this->assertStringStartsWith("--$boundary", $reqDataString);
+        $this->assertTextContains('Content-Disposition: form-data; name="h:X-MyHeader"', $reqDataString);
+        $this->assertTextContains('YouGotIt', $reqDataString);
     }
 
     public function testAttachments()
@@ -116,7 +140,7 @@ public function testAttachments()
             ->setTo('to@example.com')
             ->setAttachments([
                 'logo.png' => ['file' => TESTS . DS . 'assets' . DS . 'logo.png', 'contentId' => 'logo.png'],
-                'cake.power.gif' => ['file' => TESTS . DS . 'assets' . DS . 'cake.power.gif']
+                'cake.power.gif' => ['file' => TESTS . DS . 'assets' . DS . 'cake.power.gif'],
             ])
             ->setSubject('Email from CakePHP Mailgun plugin')
             ->send('Hello there, <br> This is an email from CakePHP Mailgun Email plugin.');