Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -1574,6 +1574,7 @@
     'PhabricatorMail' => 'applications/metamta/PhabricatorMail.php',
     'PhabricatorMailImplementationAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationAdapter.php',
     'PhabricatorMailImplementationAmazonSESAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php',
+    'PhabricatorMailImplementationMailgunAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php',
     'PhabricatorMailImplementationPHPMailerAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php',
     'PhabricatorMailImplementationPHPMailerLiteAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php',
     'PhabricatorMailImplementationSendGridAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php',
@@ -1589,6 +1590,7 @@
     'PhabricatorMailReceiver' => 'applications/metamta/receiver/PhabricatorMailReceiver.php',
     'PhabricatorMailReceiverTestCase' => 'applications/metamta/receiver/__tests__/PhabricatorMailReceiverTestCase.php',
     'PhabricatorMailReplyHandler' => 'applications/metamta/replyhandler/PhabricatorMailReplyHandler.php',
+    'PhabricatorMailgunConfigOptions' => 'applications/config/option/PhabricatorMailgunConfigOptions.php',
     'PhabricatorMailingListPHIDTypeList' => 'applications/mailinglists/phid/PhabricatorMailingListPHIDTypeList.php',
     'PhabricatorMailingListQuery' => 'applications/mailinglists/query/PhabricatorMailingListQuery.php',
     'PhabricatorMailingListSearchEngine' => 'applications/mailinglists/query/PhabricatorMailingListSearchEngine.php',
@@ -1620,6 +1622,7 @@
     'PhabricatorMetaMTAMailBody' => 'applications/metamta/view/PhabricatorMetaMTAMailBody.php',
     'PhabricatorMetaMTAMailBodyTestCase' => 'applications/metamta/view/__tests__/PhabricatorMetaMTAMailBodyTestCase.php',
     'PhabricatorMetaMTAMailTestCase' => 'applications/metamta/storage/__tests__/PhabricatorMetaMTAMailTestCase.php',
+    'PhabricatorMetaMTAMailgunReceiveController' => 'applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php',
     'PhabricatorMetaMTAMailingList' => 'applications/mailinglists/storage/PhabricatorMetaMTAMailingList.php',
     'PhabricatorMetaMTAPermanentFailureException' => 'applications/metamta/exception/PhabricatorMetaMTAPermanentFailureException.php',
     'PhabricatorMetaMTAReceivedMail' => 'applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php',
@@ -4194,6 +4197,7 @@
     'PhabricatorMacroTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
     'PhabricatorMacroViewController' => 'PhabricatorMacroController',
     'PhabricatorMailImplementationAmazonSESAdapter' => 'PhabricatorMailImplementationPHPMailerLiteAdapter',
+    'PhabricatorMailImplementationMailgunAdapter' => 'PhabricatorMailImplementationAdapter',
     'PhabricatorMailImplementationPHPMailerAdapter' => 'PhabricatorMailImplementationAdapter',
     'PhabricatorMailImplementationPHPMailerLiteAdapter' => 'PhabricatorMailImplementationAdapter',
     'PhabricatorMailImplementationSendGridAdapter' => 'PhabricatorMailImplementationAdapter',
@@ -4207,6 +4211,7 @@
     'PhabricatorMailManagementShowOutboundWorkflow' => 'PhabricatorMailManagementWorkflow',
     'PhabricatorMailManagementWorkflow' => 'PhabricatorManagementWorkflow',
     'PhabricatorMailReceiverTestCase' => 'PhabricatorTestCase',
+    'PhabricatorMailgunConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorMailingListPHIDTypeList' => 'PhabricatorPHIDType',
     'PhabricatorMailingListQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
     'PhabricatorMailingListSearchEngine' => 'PhabricatorApplicationSearchEngine',
@@ -4235,6 +4240,7 @@
     'PhabricatorMetaMTAMail' => 'PhabricatorMetaMTADAO',
     'PhabricatorMetaMTAMailBodyTestCase' => 'PhabricatorTestCase',
     'PhabricatorMetaMTAMailTestCase' => 'PhabricatorTestCase',
+    'PhabricatorMetaMTAMailgunReceiveController' => 'PhabricatorMetaMTAController',
     'PhabricatorMetaMTAMailingList' =>
     array(
       0 => 'PhabricatorMetaMTADAO',
Index: src/applications/config/option/PhabricatorMailgunConfigOptions.php
===================================================================
--- /dev/null
+++ src/applications/config/option/PhabricatorMailgunConfigOptions.php
@@ -0,0 +1,28 @@
+<?php
+
+final class PhabricatorMailgunConfigOptions
+  extends PhabricatorApplicationConfigOptions {
+
+  public function getName() {
+    return pht("Integration with Mailgun");
+  }
+
+  public function getDescription() {
+    return pht("Configure Mailgun integration.");
+  }
+
+  public function getOptions() {
+    return array(
+      $this->newOption('mailgun.api-key', 'string', null)
+        ->setMasked(true)
+        ->setDescription(pht('Mailgun API key.')),
+      $this->newOption('mailgun.domain', 'string', null)
+        ->setDescription(
+          pht(
+            'Mailgun domain name. See https://mailgun.com/cp/domains'))
+        ->addExample('mycompany.com', 'Use specific domain'),
+    );
+
+  }
+
+}
Index: src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
===================================================================
--- /dev/null
+++ src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
@@ -0,0 +1,122 @@
+<?php
+
+/**
+ * Mail adapter that uses Mailgun's web API to deliver email.
+ */
+final class PhabricatorMailImplementationMailgunAdapter
+  extends PhabricatorMailImplementationAdapter {
+
+  private $params = array();
+
+  public function setFrom($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'][] = array(
+      'email' => $email,
+      'name'  => $name,
+    );
+    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, $mimetype) {
+    // TODO: implement attachments. Requires changes in HTTPSFuture
+    throw new Exception(
+      "Mailgun adapter does not currently support attachments.");
+  }
+
+  public function addHeader($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;
+  }
+
+  public function send() {
+    $key = PhabricatorEnv::getEnvConfig('mailgun.api-key');
+    $domain = PhabricatorEnv::getEnvConfig('mailgun.domain');
+    $params = array();
+
+    $params['to'] = idx($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'] = $replyto;
+    }
+
+    if (idx($this->params, 'ccs')) {
+      $params['cc'] = $this->params['ccs'];
+    }
+
+    $future = new HTTPSFuture(
+      "https://api:{$key}@api.mailgun.net/v2/{$domain}/messages",
+      $params);
+    $future->setMethod('POST');
+
+    list($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;
+  }
+
+}
Index: src/applications/metamta/application/PhabricatorApplicationMetaMTA.php
===================================================================
--- src/applications/metamta/application/PhabricatorApplicationMetaMTA.php
+++ src/applications/metamta/application/PhabricatorApplicationMetaMTA.php
@@ -34,6 +34,7 @@
     return array(
       $this->getBaseURI() => array(
         'sendgrid/' => 'PhabricatorMetaMTASendGridReceiveController',
+        'mailgun/' => 'PhabricatorMetaMTAMailgunReceiveController',
       ),
     );
   }
Index: src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php
===================================================================
--- /dev/null
+++ src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php
@@ -0,0 +1,76 @@
+<?php
+
+final class PhabricatorMetaMTAMailgunReceiveController
+  extends PhabricatorMetaMTAController {
+
+  public function shouldRequireLogin() {
+    return false;
+  }
+
+  private function verifyMessage() {
+    $api_key = PhabricatorEnv::getEnvConfig('mailgun.api-key');
+    $request = $this->getRequest();
+    $timestamp = $request->getStr('timestamp');
+    $token = $request->getStr('token');
+    $sig = $request->getStr('signature');
+    return hash_hmac('sha256', $timestamp.$token, $api_key) == $sig;
+
+  }
+  public function processRequest() {
+
+    // No CSRF for Mailgun.
+    $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
+
+    if (!$this->verifyMessage()) {
+      throw new Exception(
+        'Mail signature is not valid. Check your Mailgun API key.');
+    }
+
+    $request = $this->getRequest();
+    $user = $request->getUser();
+
+    $raw_headers = $request->getStr('headers');
+    $raw_headers = explode("\n", rtrim($raw_headers));
+    $raw_dict = array();
+    foreach (array_filter($raw_headers) as $header) {
+      list($name, $value) = explode(':', $header, 2);
+      $raw_dict[$name] = ltrim($value);
+    }
+
+    $headers = array(
+      'to'      => $request->getStr('recipient'),
+      'from'    => $request->getStr('from'),
+      'subject' => $request->getStr('subject'),
+    ) + $raw_dict;
+
+    $received = new PhabricatorMetaMTAReceivedMail();
+    $received->setHeaders($headers);
+    $received->setBodies(array(
+      'text' => $request->getStr('stripped-text'),
+      'html' => $request->getStr('stripped-html'),
+    ));
+
+    $file_phids = array();
+    foreach ($_FILES as $file_raw) {
+      try {
+        $file = PhabricatorFile::newFromPHPUpload(
+          $file_raw,
+          array(
+            'authorPHID' => $user->getPHID(),
+          ));
+        $file_phids[] = $file->getPHID();
+      } catch (Exception $ex) {
+        phlog($ex);
+      }
+    }
+    $received->setAttachments($file_phids);
+    $received->save();
+
+    $received->processReceivedMail();
+
+    $response = new AphrontWebpageResponse();
+    $response->setContent(pht("Got it! Thanks, Mailgun!\n"));
+    return $response;
+  }
+
+}