diff --git a/src/MailtrapTransport.php b/src/MailtrapTransport.php
index ee36f6e..50b9246 100644
--- a/src/MailtrapTransport.php
+++ b/src/MailtrapTransport.php
@@ -68,6 +68,7 @@ public function send(Swift_Mime_SimpleMessage $message, &$failedRecipients = nul
      */
     protected function payload(Swift_Mime_SimpleMessage $message): array
     {
+        // Process addresses for mail
         $payload = [
             'headers' => [
                 'Api-Token' => $this->token,
@@ -86,6 +87,7 @@ protected function payload(Swift_Mime_SimpleMessage $message): array
             $payload['json']['bcc'] = $this->processAddresses($message->getBcc());
         }
 
+        // Process body content and attachments
         if (count($message->getChildren())) {
             // We're dealing with a multipart message
             if ($message->getBodyContentType() === 'text/html') {
@@ -120,6 +122,12 @@ protected function payload(Swift_Mime_SimpleMessage $message): array
             $payload['json']['text'] = $message->getBody();
         }
 
+        // Add category if it's available
+        if ($message->getHeaders()->has('X-Mailtrap-Category')) {
+            $payload['json']['category'] = $message->getHeaders()->get('X-Mailtrap-Category')->getFieldBody();
+            $message->getHeaders()->remove('X-Mailtrap-Category');
+        }
+
         return $payload;
     }
 
diff --git a/tests/MailtrapTransportTest.php b/tests/MailtrapTransportTest.php
index 1f8b3d9..96b6ab4 100644
--- a/tests/MailtrapTransportTest.php
+++ b/tests/MailtrapTransportTest.php
@@ -21,6 +21,69 @@ public function testCanGetTransport()
         );
     }
 
+    public function testCanSendPlainEmailWithCategory()
+    {
+        // Mock client
+        $client = \Mockery::mock(\GuzzleHttp\ClientInterface::class);
+        $driver = $this->app['swift.transport']->driver('mailtrap');
+        $driver->setClient($client);
+
+        $args = [];
+        $client
+            ->shouldReceive('request')
+            ->once()
+            ->andReturnUsing(function (...$params) use (&$args) {
+                $args = $params;
+
+                $body = \Mockery::mock(\Psr\Http\Message\StreamInterface::class);
+                $body->shouldReceive('getContents')->andReturn(json_encode([
+                    'success' => true,
+                    'message_ids' => [
+                        123
+                    ],
+                ]));
+
+                $response = \Mockery::mock(\Psr\Http\Message\ResponseInterface::class);
+                $response->shouldReceive('getBody')->andReturn($body);
+
+                return $response;
+            });
+
+        /** @var \Illuminate\Mail\Mailer */
+        $mailer = $this->app['mailer'];
+
+        // Send test email
+        $mailer->raw('Hello World', function ($mail) {
+            $mail
+                ->to('ben@manageit.com.au')
+                ->subject('Test email');
+
+            $mail->getHeaders()->addTextHeader(
+                'X-Mailtrap-Category',
+                'test'
+            );
+        });
+
+        // Check arguments passed to Guzzle
+        $this->assertEquals('POST', $args[0]);
+        $this->assertEquals('https://send.api.mailtrap.io/api/send', $args[1]);
+
+        // Check payload
+        $payload = $args[2];
+        $this->assertEquals('foo', $payload['headers']['Api-Token']);
+        $this->assertEquals([
+            'email' => 'example@manageit.com.au',
+            'name' => 'Manage It',
+        ], $payload['json']['from']);
+        $this->assertEquals([
+            'email' => 'ben@manageit.com.au',
+        ], $payload['json']['to'][0]);
+        $this->assertEquals('Test email', $payload['json']['subject']);
+        $this->assertEquals('test', $payload['json']['category']);
+        $this->assertEquals('Hello World', $payload['json']['text']);
+        $this->assertArrayNotHasKey('html', $payload['json']);
+    }
+
     public function testCanSendHtmlEmail()
     {
         // Mock client
@@ -34,7 +97,19 @@ public function testCanSendHtmlEmail()
             ->once()
             ->andReturnUsing(function (...$params) use (&$args) {
                 $args = $params;
-                return \Mockery::mock(\Psr\Http\Message\ResponseInterface::class);
+
+                $body = \Mockery::mock(\Psr\Http\Message\StreamInterface::class);
+                $body->shouldReceive('getContents')->andReturn(json_encode([
+                    'success' => true,
+                    'message_ids' => [
+                        123
+                    ],
+                ]));
+
+                $response = \Mockery::mock(\Psr\Http\Message\ResponseInterface::class);
+                $response->shouldReceive('getBody')->andReturn($body);
+
+                return $response;
             });
 
         /** @var \Illuminate\Mail\Mailer */
@@ -63,6 +138,7 @@ public function testCanSendHtmlEmail()
         ], $payload['json']['to'][0]);
         $this->assertEquals('Test email', $payload['json']['subject']);
         $this->assertEquals('<h1>Hello World</h1>', $payload['json']['html']);
+        $this->assertArrayNotHasKey('text', $payload['json']);
     }
 
     public function testCanSendMailable()
@@ -78,7 +154,19 @@ public function testCanSendMailable()
             ->once()
             ->andReturnUsing(function (...$params) use (&$args) {
                 $args = $params;
-                return \Mockery::mock(\Psr\Http\Message\ResponseInterface::class);
+
+                $body = \Mockery::mock(\Psr\Http\Message\StreamInterface::class);
+                $body->shouldReceive('getContents')->andReturn(json_encode([
+                    'success' => true,
+                    'message_ids' => [
+                        123
+                    ],
+                ]));
+
+                $response = \Mockery::mock(\Psr\Http\Message\ResponseInterface::class);
+                $response->shouldReceive('getBody')->andReturn($body);
+
+                return $response;
             });
 
         /** @var \Illuminate\Mail\Mailer */