diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
index c7cd05753b..1dd65673bf 100644
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
@@ -1,137 +1,137 @@
 <?php
 
 /**
  * Mail adapter that uses Mailgun's web API to deliver email.
  */
 final class PhabricatorMailImplementationMailgunAdapter
   extends PhabricatorMailImplementationAdapter {
 
   private $params = array();
   private $attachments = array();
 
   public function setFrom($email, $name = '') {
     $this->params['from'] = $email;
     $this->params['from-name'] = $name;
     return $this;
   }
 
   public function addReplyTo($email, $name = '') {
     if (empty($this->params['reply-to'])) {
       $this->params['reply-to'] = array();
     }
     $this->params['reply-to'][] = "{$name} <{$email}>";
     return $this;
   }
 
   public function addTos(array $emails) {
     foreach ($emails as $email) {
       $this->params['tos'][] = $email;
     }
     return $this;
   }
 
   public function addCCs(array $emails) {
     foreach ($emails as $email) {
       $this->params['ccs'][] = $email;
     }
     return $this;
   }
 
   public function addAttachment($data, $filename, $mimetype) {
     $this->attachments[] = array(
       'data' => $data,
       'name' => $filename,
       'type' => $mimetype,
     );
 
     return $this;
   }
 
   public function addHeader($header_name, $header_value) {
     $this->params['headers'][] = array($header_name, $header_value);
     return $this;
   }
 
   public function setBody($body) {
     $this->params['body'] = $body;
     return $this;
   }
 
   public function setSubject($subject) {
     $this->params['subject'] = $subject;
     return $this;
   }
 
   public function setIsHTML($is_html) {
     $this->params['is-html'] = $is_html;
     return $this;
   }
 
   public function supportsMessageIDHeader() {
-    return false;
+    return true;
   }
 
   public function send() {
     $key = PhabricatorEnv::getEnvConfig('mailgun.api-key');
     $domain = PhabricatorEnv::getEnvConfig('mailgun.domain');
     $params = array();
 
     $params['to'] = implode(', ', idx($this->params, 'tos', array()));
     $params['subject'] = idx($this->params, 'subject');
 
     if (idx($this->params, 'is-html')) {
       $params['html'] = idx($this->params, 'body');
     } else {
       $params['text'] = idx($this->params, 'body');
     }
 
     $from = idx($this->params, 'from');
     if (idx($this->params, 'from-name')) {
       $params['from'] = "{$this->params['from-name']} <{$from}>";
     } else {
       $params['from'] = $from;
     }
 
     if (idx($this->params, 'reply-to')) {
       $replyto = $this->params['reply-to'];
       $params['h:reply-to'] = implode(', ', $replyto);
     }
 
     if (idx($this->params, 'ccs')) {
       $params['cc'] = implode(', ', $this->params['ccs']);
     }
 
     foreach (idx($this->params, 'headers', array()) as $header) {
       list($name, $value) = $header;
       $params['h:'.$name] = $value;
     }
 
     $future = new HTTPSFuture(
       "https://api:{$key}@api.mailgun.net/v2/{$domain}/messages",
       $params);
     $future->setMethod('POST');
 
     foreach ($this->attachments as $attachment) {
       $future->attachFileData(
         'attachment',
         $attachment['data'],
         $attachment['name'],
         $attachment['type']);
     }
 
     list($body) = $future->resolvex();
 
     $response = json_decode($body, true);
     if (!is_array($response)) {
       throw new Exception("Failed to JSON decode response: {$body}");
     }
 
     if (!idx($response, 'id')) {
       $message = $response['message'];
       throw new Exception("Request failed with errors: {$message}.");
     }
 
     return true;
   }
 
 }