diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -3387,6 +3387,8 @@
     'PhabricatorMacroTransactionQuery' => 'applications/macro/query/PhabricatorMacroTransactionQuery.php',
     'PhabricatorMacroTransactionType' => 'applications/macro/xaction/PhabricatorMacroTransactionType.php',
     'PhabricatorMacroViewController' => 'applications/macro/controller/PhabricatorMacroViewController.php',
+    'PhabricatorMailAdapter' => 'applications/metamta/adapter/PhabricatorMailAdapter.php',
+    'PhabricatorMailAmazonSESAdapter' => 'applications/metamta/adapter/PhabricatorMailAmazonSESAdapter.php',
     'PhabricatorMailAttachment' => 'applications/metamta/message/PhabricatorMailAttachment.php',
     'PhabricatorMailConfigTestCase' => 'applications/metamta/storage/__tests__/PhabricatorMailConfigTestCase.php',
     'PhabricatorMailEmailEngine' => 'applications/metamta/engine/PhabricatorMailEmailEngine.php',
@@ -3397,14 +3399,7 @@
     'PhabricatorMailEngineExtension' => 'applications/metamta/engine/PhabricatorMailEngineExtension.php',
     'PhabricatorMailExternalMessage' => 'applications/metamta/message/PhabricatorMailExternalMessage.php',
     'PhabricatorMailHeader' => 'applications/metamta/message/PhabricatorMailHeader.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',
-    'PhabricatorMailImplementationPostmarkAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationPostmarkAdapter.php',
-    'PhabricatorMailImplementationSendGridAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php',
-    'PhabricatorMailImplementationTestAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php',
+    'PhabricatorMailMailgunAdapter' => 'applications/metamta/adapter/PhabricatorMailMailgunAdapter.php',
     'PhabricatorMailManagementListInboundWorkflow' => 'applications/metamta/management/PhabricatorMailManagementListInboundWorkflow.php',
     'PhabricatorMailManagementListOutboundWorkflow' => 'applications/metamta/management/PhabricatorMailManagementListOutboundWorkflow.php',
     'PhabricatorMailManagementReceiveTestWorkflow' => 'applications/metamta/management/PhabricatorMailManagementReceiveTestWorkflow.php',
@@ -3422,14 +3417,19 @@
     'PhabricatorMailOutboundRoutingSelfEmailHeraldAction' => 'applications/metamta/herald/PhabricatorMailOutboundRoutingSelfEmailHeraldAction.php',
     'PhabricatorMailOutboundRoutingSelfNotificationHeraldAction' => 'applications/metamta/herald/PhabricatorMailOutboundRoutingSelfNotificationHeraldAction.php',
     'PhabricatorMailOutboundStatus' => 'applications/metamta/constants/PhabricatorMailOutboundStatus.php',
+    'PhabricatorMailPHPMailerAdapter' => 'applications/metamta/adapter/PhabricatorMailPHPMailerAdapter.php',
+    'PhabricatorMailPHPMailerLiteAdapter' => 'applications/metamta/adapter/PhabricatorMailPHPMailerLiteAdapter.php',
+    'PhabricatorMailPostmarkAdapter' => 'applications/metamta/adapter/PhabricatorMailPostmarkAdapter.php',
     'PhabricatorMailPropertiesDestructionEngineExtension' => 'applications/metamta/engineextension/PhabricatorMailPropertiesDestructionEngineExtension.php',
     'PhabricatorMailReceiver' => 'applications/metamta/receiver/PhabricatorMailReceiver.php',
     'PhabricatorMailReceiverTestCase' => 'applications/metamta/receiver/__tests__/PhabricatorMailReceiverTestCase.php',
     'PhabricatorMailReplyHandler' => 'applications/metamta/replyhandler/PhabricatorMailReplyHandler.php',
     'PhabricatorMailRoutingRule' => 'applications/metamta/constants/PhabricatorMailRoutingRule.php',
+    'PhabricatorMailSendGridAdapter' => 'applications/metamta/adapter/PhabricatorMailSendGridAdapter.php',
     'PhabricatorMailSetupCheck' => 'applications/config/check/PhabricatorMailSetupCheck.php',
     'PhabricatorMailStamp' => 'applications/metamta/stamp/PhabricatorMailStamp.php',
     'PhabricatorMailTarget' => 'applications/metamta/replyhandler/PhabricatorMailTarget.php',
+    'PhabricatorMailTestAdapter' => 'applications/metamta/adapter/PhabricatorMailTestAdapter.php',
     'PhabricatorMailUtil' => 'applications/metamta/util/PhabricatorMailUtil.php',
     'PhabricatorMainMenuBarExtension' => 'view/page/menu/PhabricatorMainMenuBarExtension.php',
     'PhabricatorMainMenuSearchView' => 'view/page/menu/PhabricatorMainMenuSearchView.php',
@@ -9221,6 +9221,8 @@
     'PhabricatorMacroTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
     'PhabricatorMacroTransactionType' => 'PhabricatorModularTransactionType',
     'PhabricatorMacroViewController' => 'PhabricatorMacroController',
+    'PhabricatorMailAdapter' => 'Phobject',
+    'PhabricatorMailAmazonSESAdapter' => 'PhabricatorMailPHPMailerLiteAdapter',
     'PhabricatorMailAttachment' => 'Phobject',
     'PhabricatorMailConfigTestCase' => 'PhabricatorTestCase',
     'PhabricatorMailEmailEngine' => 'PhabricatorMailMessageEngine',
@@ -9231,14 +9233,7 @@
     'PhabricatorMailEngineExtension' => 'Phobject',
     'PhabricatorMailExternalMessage' => 'Phobject',
     'PhabricatorMailHeader' => 'Phobject',
-    'PhabricatorMailImplementationAdapter' => 'Phobject',
-    'PhabricatorMailImplementationAmazonSESAdapter' => 'PhabricatorMailImplementationPHPMailerLiteAdapter',
-    'PhabricatorMailImplementationMailgunAdapter' => 'PhabricatorMailImplementationAdapter',
-    'PhabricatorMailImplementationPHPMailerAdapter' => 'PhabricatorMailImplementationAdapter',
-    'PhabricatorMailImplementationPHPMailerLiteAdapter' => 'PhabricatorMailImplementationAdapter',
-    'PhabricatorMailImplementationPostmarkAdapter' => 'PhabricatorMailImplementationAdapter',
-    'PhabricatorMailImplementationSendGridAdapter' => 'PhabricatorMailImplementationAdapter',
-    'PhabricatorMailImplementationTestAdapter' => 'PhabricatorMailImplementationAdapter',
+    'PhabricatorMailMailgunAdapter' => 'PhabricatorMailAdapter',
     'PhabricatorMailManagementListInboundWorkflow' => 'PhabricatorMailManagementWorkflow',
     'PhabricatorMailManagementListOutboundWorkflow' => 'PhabricatorMailManagementWorkflow',
     'PhabricatorMailManagementReceiveTestWorkflow' => 'PhabricatorMailManagementWorkflow',
@@ -9256,14 +9251,19 @@
     'PhabricatorMailOutboundRoutingSelfEmailHeraldAction' => 'PhabricatorMailOutboundRoutingHeraldAction',
     'PhabricatorMailOutboundRoutingSelfNotificationHeraldAction' => 'PhabricatorMailOutboundRoutingHeraldAction',
     'PhabricatorMailOutboundStatus' => 'Phobject',
+    'PhabricatorMailPHPMailerAdapter' => 'PhabricatorMailAdapter',
+    'PhabricatorMailPHPMailerLiteAdapter' => 'PhabricatorMailAdapter',
+    'PhabricatorMailPostmarkAdapter' => 'PhabricatorMailAdapter',
     'PhabricatorMailPropertiesDestructionEngineExtension' => 'PhabricatorDestructionEngineExtension',
     'PhabricatorMailReceiver' => 'Phobject',
     'PhabricatorMailReceiverTestCase' => 'PhabricatorTestCase',
     'PhabricatorMailReplyHandler' => 'Phobject',
     'PhabricatorMailRoutingRule' => 'Phobject',
+    'PhabricatorMailSendGridAdapter' => 'PhabricatorMailAdapter',
     'PhabricatorMailSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorMailStamp' => 'Phobject',
     'PhabricatorMailTarget' => 'Phobject',
+    'PhabricatorMailTestAdapter' => 'PhabricatorMailAdapter',
     'PhabricatorMailUtil' => 'Phobject',
     'PhabricatorMainMenuBarExtension' => 'Phobject',
     'PhabricatorMainMenuSearchView' => 'AphrontView',
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationAdapter.php b/src/applications/metamta/adapter/PhabricatorMailAdapter.php
rename from src/applications/metamta/adapter/PhabricatorMailImplementationAdapter.php
rename to src/applications/metamta/adapter/PhabricatorMailAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailAdapter.php
@@ -1,13 +1,16 @@
 <?php
 
-abstract class PhabricatorMailImplementationAdapter extends Phobject {
+abstract class PhabricatorMailAdapter
+  extends Phobject {
 
   private $key;
   private $priority;
+  private $media;
   private $options = array();
 
   private $supportsInbound = true;
   private $supportsOutbound = true;
+  private $mediaMap;
 
   final public function getAdapterType() {
     return $this->getPhobjectClassConstant('ADAPTERTYPE');
@@ -20,37 +23,67 @@
       ->execute();
   }
 
+  /* abstract */ public function getSupportedMessageTypes() {
+    throw new PhutilMethodNotImplementedException();
+  }
 
-  abstract public function setFrom($email, $name = '');
-  abstract public function addReplyTo($email, $name = '');
-  abstract public function addTos(array $emails);
-  abstract public function addCCs(array $emails);
-  abstract public function addAttachment($data, $filename, $mimetype);
-  abstract public function addHeader($header_name, $header_value);
-  abstract public function setBody($plaintext_body);
-  abstract public function setHTMLBody($html_body);
-  abstract public function setSubject($subject);
-
+  /* abstract */ public function sendMessage(
+    PhabricatorMailExternalMessage $message) {
+    throw new PhutilMethodNotImplementedException();
+  }
 
   /**
-   * Some mailers, notably Amazon SES, do not support us setting a specific
-   * Message-ID header.
+   * Return true if this adapter supports setting a "Message-ID" when sending
+   * email.
+   *
+   * This is an ugly implementation detail because mail threading is a horrible
+   * mess, implemented differently by every client in existence.
    */
-  abstract public function supportsMessageIDHeader();
+  public function supportsMessageIDHeader() {
+    return false;
+  }
 
+  final public function supportsMessageType($message_type) {
+    if ($this->mediaMap === null) {
+      $media_map = $this->getSupportedMessageTypes();
+      $media_map = array_fuse($media_map);
 
-  /**
-   * Send the message. Generally, this means connecting to some service and
-   * handing data to it.
-   *
-   * If the adapter determines that the mail will never be deliverable, it
-   * should throw a @{class:PhabricatorMetaMTAPermanentFailureException}.
-   *
-   * For temporary failures, throw some other exception or return `false`.
-   *
-   * @return bool True on success.
-   */
-  abstract public function send();
+      if ($this->media) {
+        $config_map = $this->media;
+        $config_map = array_fuse($config_map);
+
+        $media_map = array_intersect_key($media_map, $config_map);
+      }
+
+      $this->mediaMap = $media_map;
+    }
+
+    return isset($this->mediaMap[$message_type]);
+  }
+
+  final public function setMedia(array $media) {
+    $native_map = $this->getSupportedMessageTypes();
+    $native_map = array_fuse($native_map);
+
+    foreach ($media as $medium) {
+      if (!isset($native_map[$medium])) {
+        throw new Exception(
+          pht(
+            'Adapter ("%s") is configured for medium "%s", but this is not '.
+            'a supported delivery medium. Supported media are: %s.',
+            $medium,
+            implode(', ', $native_map)));
+      }
+    }
+
+    $this->media = $media;
+    $this->mediaMap = null;
+    return $this;
+  }
+
+  final public function getMedia() {
+    return $this->media;
+  }
 
   final public function setKey($key) {
     $this->key = $key;
@@ -110,18 +143,4 @@
 
   abstract public function newDefaultOptions();
 
-  public function prepareForSend() {
-    return;
-  }
-
-  protected function renderAddress($email, $name = null) {
-    if (strlen($name)) {
-      return (string)id(new PhutilEmailAddress())
-        ->setDisplayName($name)
-        ->setAddress($email);
-    } else {
-      return $email;
-    }
-  }
-
 }
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php b/src/applications/metamta/adapter/PhabricatorMailAmazonSESAdapter.php
rename from src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php
rename to src/applications/metamta/adapter/PhabricatorMailAmazonSESAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailAmazonSESAdapter.php
@@ -1,7 +1,7 @@
 <?php
 
-final class PhabricatorMailImplementationAmazonSESAdapter
-  extends PhabricatorMailImplementationPHPMailerLiteAdapter {
+final class PhabricatorMailAmazonSESAdapter
+  extends PhabricatorMailPHPMailerLiteAdapter {
 
   const ADAPTERTYPE = 'ses';
 
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationPostmarkAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationPostmarkAdapter.php
deleted file mode 100644
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationPostmarkAdapter.php
+++ /dev/null
@@ -1,120 +0,0 @@
-<?php
-
-final class PhabricatorMailImplementationPostmarkAdapter
-  extends PhabricatorMailImplementationAdapter {
-
-  const ADAPTERTYPE = 'postmark';
-
-  private $parameters = array();
-
-  public function setFrom($email, $name = '') {
-    $this->parameters['From'] = $this->renderAddress($email, $name);
-    return $this;
-  }
-
-  public function addReplyTo($email, $name = '') {
-    $this->parameters['ReplyTo'] = $this->renderAddress($email, $name);
-    return $this;
-  }
-
-  public function addTos(array $emails) {
-    foreach ($emails as $email) {
-      $this->parameters['To'][] = $email;
-    }
-    return $this;
-  }
-
-  public function addCCs(array $emails) {
-    foreach ($emails as $email) {
-      $this->parameters['Cc'][] = $email;
-    }
-    return $this;
-  }
-
-  public function addAttachment($data, $filename, $mimetype) {
-    $this->parameters['Attachments'][] = array(
-      'Name' => $filename,
-      'ContentType' => $mimetype,
-      'Content' => base64_encode($data),
-    );
-
-    return $this;
-  }
-
-  public function addHeader($header_name, $header_value) {
-    $this->parameters['Headers'][] = array(
-      'Name' => $header_name,
-      'Value' => $header_value,
-    );
-    return $this;
-  }
-
-  public function setBody($body) {
-    $this->parameters['TextBody'] = $body;
-    return $this;
-  }
-
-  public function setHTMLBody($html_body) {
-    $this->parameters['HtmlBody'] = $html_body;
-    return $this;
-  }
-
-  public function setSubject($subject) {
-    $this->parameters['Subject'] = $subject;
-    return $this;
-  }
-
-  public function supportsMessageIDHeader() {
-    return true;
-  }
-
-  protected function validateOptions(array $options) {
-    PhutilTypeSpec::checkMap(
-      $options,
-      array(
-        'access-token' => 'string',
-        'inbound-addresses' => 'list<string>',
-      ));
-
-    // Make sure this is properly formatted.
-    PhutilCIDRList::newList($options['inbound-addresses']);
-  }
-
-  public function newDefaultOptions() {
-    return array(
-      'access-token' => null,
-      'inbound-addresses' => array(
-        // Via Postmark support circa February 2018, see:
-        //
-        // https://postmarkapp.com/support/article/800-ips-for-firewalls
-        //
-        // "Configuring Outbound Email" should be updated if this changes.
-        '50.31.156.6/32',
-      ),
-    );
-  }
-
-  public function send() {
-    $access_token = $this->getOption('access-token');
-
-    $parameters = $this->parameters;
-    $flatten = array(
-      'To',
-      'Cc',
-    );
-
-    foreach ($flatten as $key) {
-      if (isset($parameters[$key])) {
-        $parameters[$key] = implode(', ', $parameters[$key]);
-      }
-    }
-
-    id(new PhutilPostmarkFuture())
-      ->setAccessToken($access_token)
-      ->setMethod('email', $parameters)
-      ->resolve();
-
-    return true;
-  }
-
-}
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php b/src/applications/metamta/adapter/PhabricatorMailMailgunAdapter.php
rename from src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
rename to src/applications/metamta/adapter/PhabricatorMailMailgunAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailMailgunAdapter.php
@@ -3,8 +3,8 @@
 /**
  * Mail adapter that uses Mailgun's web API to deliver email.
  */
-final class PhabricatorMailImplementationMailgunAdapter
-  extends PhabricatorMailImplementationAdapter {
+final class PhabricatorMailMailgunAdapter
+  extends PhabricatorMailAdapter {
 
   const ADAPTERTYPE = 'mailgun';
 
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php b/src/applications/metamta/adapter/PhabricatorMailPHPMailerAdapter.php
rename from src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php
rename to src/applications/metamta/adapter/PhabricatorMailPHPMailerAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailPHPMailerAdapter.php
@@ -1,7 +1,7 @@
 <?php
 
-final class PhabricatorMailImplementationPHPMailerAdapter
-  extends PhabricatorMailImplementationAdapter {
+final class PhabricatorMailPHPMailerAdapter
+  extends PhabricatorMailAdapter {
 
   const ADAPTERTYPE = 'smtp';
 
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php b/src/applications/metamta/adapter/PhabricatorMailPHPMailerLiteAdapter.php
rename from src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php
rename to src/applications/metamta/adapter/PhabricatorMailPHPMailerLiteAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailPHPMailerLiteAdapter.php
@@ -2,9 +2,11 @@
 
 /**
  * TODO: Should be final, but inherited by SES.
+ *
+ * @concrete-extensible
  */
-class PhabricatorMailImplementationPHPMailerLiteAdapter
-  extends PhabricatorMailImplementationAdapter {
+class PhabricatorMailPHPMailerLiteAdapter
+  extends PhabricatorMailAdapter {
 
   const ADAPTERTYPE = 'sendmail';
 
diff --git a/src/applications/metamta/adapter/PhabricatorMailPostmarkAdapter.php b/src/applications/metamta/adapter/PhabricatorMailPostmarkAdapter.php
new file mode 100644
--- /dev/null
+++ b/src/applications/metamta/adapter/PhabricatorMailPostmarkAdapter.php
@@ -0,0 +1,128 @@
+<?php
+
+final class PhabricatorMailPostmarkAdapter
+  extends PhabricatorMailAdapter {
+
+  const ADAPTERTYPE = 'postmark';
+
+  public function getSupportedMessageTypes() {
+    return array(
+      PhabricatorMailEmailMessage::MESSAGETYPE,
+    );
+  }
+
+  public function supportsMessageIDHeader() {
+    return true;
+  }
+
+  protected function validateOptions(array $options) {
+    PhutilTypeSpec::checkMap(
+      $options,
+      array(
+        'access-token' => 'string',
+        'inbound-addresses' => 'list<string>',
+      ));
+
+    // Make sure this is properly formatted.
+    PhutilCIDRList::newList($options['inbound-addresses']);
+  }
+
+  public function newDefaultOptions() {
+    return array(
+      'access-token' => null,
+      'inbound-addresses' => array(
+        // Via Postmark support circa February 2018, see:
+        //
+        // https://postmarkapp.com/support/article/800-ips-for-firewalls
+        //
+        // "Configuring Outbound Email" should be updated if this changes.
+        //
+        // These addresses were last updated in January 2019.
+        '50.31.156.6/32',
+        '50.31.156.77/32',
+        '18.217.206.57/32',
+      ),
+    );
+  }
+
+  public function sendMessage(PhabricatorMailExternalMessage $message) {
+    $access_token = $this->getOption('access-token');
+
+    $parameters = array();
+
+    $subject = $message->getSubject();
+    if ($subject !== null) {
+      $parameters['Subject'] = $subject;
+    }
+
+    $from_address = $message->getFromAddress();
+    if ($from_address) {
+      $parameters['From'] = (string)$from_address;
+    }
+
+    $to_addresses = $message->getToAddresses();
+    if ($to_addresses) {
+      $to = array();
+      foreach ($to_addresses as $address) {
+        $to[] = (string)$address;
+      }
+      $parameters['To'] = implode(', ', $to);
+    }
+
+    $cc_addresses = $message->getCCAddresses();
+    if ($cc_addresses) {
+      $cc = array();
+      foreach ($cc_addresses as $address) {
+        $cc[] = (string)$address;
+      }
+      $parameters['Cc'] = implode(', ', $cc);
+    }
+
+    $reply_address = $message->getReplyToAddress();
+    if ($reply_address) {
+      $parameters['ReplyTo'] = (string)$reply_address;
+    }
+
+    $headers = $message->getHeaders();
+    if ($headers) {
+      $list = array();
+      foreach ($headers as $header) {
+        $list[] = array(
+          'Name' => $header->getName(),
+          'Value' => $header->getValue(),
+        );
+      }
+      $parameters['Headers'] = $list;
+    }
+
+    $text_body = $message->getTextBody();
+    if ($text_body !== null) {
+      $parameters['TextBody'] = $text_body;
+    }
+
+    $html_body = $message->getHTMLBody();
+    if ($html_body !== null) {
+      $parameters['HtmlBody'] = $html_body;
+    }
+
+    $attachments = $message->getAttachments();
+    if ($attachments) {
+      $files = array();
+      foreach ($attachments as $attachment) {
+        $files[] = array(
+          'Name' => $attachment->getFilename(),
+          'ContentType' => $attachment->getMimeType(),
+          'Content' => base64_encode($attachment->getData()),
+        );
+      }
+      $parameters['Attachments'] = $files;
+    }
+
+    id(new PhutilPostmarkFuture())
+      ->setAccessToken($access_token)
+      ->setMethod('email', $parameters)
+      ->setTimeout(60)
+      ->resolve();
+  }
+
+}
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php b/src/applications/metamta/adapter/PhabricatorMailSendGridAdapter.php
rename from src/applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php
rename to src/applications/metamta/adapter/PhabricatorMailSendGridAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailSendGridAdapter.php
@@ -3,8 +3,8 @@
 /**
  * Mail adapter that uses SendGrid's web API to deliver email.
  */
-final class PhabricatorMailImplementationSendGridAdapter
-  extends PhabricatorMailImplementationAdapter {
+final class PhabricatorMailSendGridAdapter
+  extends PhabricatorMailAdapter {
 
   const ADAPTERTYPE = 'sendgrid';
 
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php b/src/applications/metamta/adapter/PhabricatorMailTestAdapter.php
rename from src/applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php
rename to src/applications/metamta/adapter/PhabricatorMailTestAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailTestAdapter.php
@@ -4,8 +4,8 @@
  * Mail adapter that doesn't actually send any email, for writing unit tests
  * against.
  */
-final class PhabricatorMailImplementationTestAdapter
-  extends PhabricatorMailImplementationAdapter {
+final class PhabricatorMailTestAdapter
+  extends PhabricatorMailAdapter {
 
   const ADAPTERTYPE = 'test';
 
diff --git a/src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php b/src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php
--- a/src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php
+++ b/src/applications/metamta/controller/PhabricatorMetaMTAMailgunReceiveController.php
@@ -21,7 +21,7 @@
       array(
         'inbound' => true,
         'types' => array(
-          PhabricatorMailImplementationMailgunAdapter::ADAPTERTYPE,
+          PhabricatorMailMailgunAdapter::ADAPTERTYPE,
         ),
       ));
     foreach ($mailers as $mailer) {
diff --git a/src/applications/metamta/controller/PhabricatorMetaMTAPostmarkReceiveController.php b/src/applications/metamta/controller/PhabricatorMetaMTAPostmarkReceiveController.php
--- a/src/applications/metamta/controller/PhabricatorMetaMTAPostmarkReceiveController.php
+++ b/src/applications/metamta/controller/PhabricatorMetaMTAPostmarkReceiveController.php
@@ -16,7 +16,7 @@
       array(
         'inbound' => true,
         'types' => array(
-          PhabricatorMailImplementationPostmarkAdapter::ADAPTERTYPE,
+          PhabricatorMailPostmarkAdapter::ADAPTERTYPE,
         ),
       ));
     if (!$mailers) {
diff --git a/src/applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php b/src/applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php
--- a/src/applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php
+++ b/src/applications/metamta/controller/PhabricatorMetaMTASendGridReceiveController.php
@@ -15,7 +15,7 @@
       array(
         'inbound' => true,
         'types' => array(
-          PhabricatorMailImplementationSendGridAdapter::ADAPTERTYPE,
+          PhabricatorMailSendGridAdapter::ADAPTERTYPE,
         ),
       ));
     if (!$mailers) {
diff --git a/src/applications/metamta/engine/PhabricatorMailMessageEngine.php b/src/applications/metamta/engine/PhabricatorMailMessageEngine.php
--- a/src/applications/metamta/engine/PhabricatorMailMessageEngine.php
+++ b/src/applications/metamta/engine/PhabricatorMailMessageEngine.php
@@ -8,8 +8,7 @@
   private $actors = array();
   private $preferences;
 
-  final public function setMailer(
-    PhabricatorMailImplementationAdapter $mailer) {
+  final public function setMailer(PhabricatorMailAdapter $mailer) {
 
     $this->mailer = $mailer;
     return $this;
diff --git a/src/applications/metamta/storage/PhabricatorMetaMTAMail.php b/src/applications/metamta/storage/PhabricatorMetaMTAMail.php
--- a/src/applications/metamta/storage/PhabricatorMetaMTAMail.php
+++ b/src/applications/metamta/storage/PhabricatorMetaMTAMail.php
@@ -547,13 +547,14 @@
         'types' => 'optional list<string>',
         'inbound' => 'optional bool',
         'outbound' => 'optional bool',
+        'media' => 'optional list<string>',
       ));
 
     $mailers = array();
 
     $config = PhabricatorEnv::getEnvConfig('cluster.mailers');
 
-    $adapters = PhabricatorMailImplementationAdapter::getAllAdapters();
+    $adapters = PhabricatorMailAdapter::getAllAdapters();
     $next_priority = -1;
 
     foreach ($config as $spec) {
@@ -583,6 +584,11 @@
       $mailer->setSupportsInbound(idx($spec, 'inbound', true));
       $mailer->setSupportsOutbound(idx($spec, 'outbound', true));
 
+      $media = idx($spec, 'media');
+      if ($media !== null) {
+        $mailer->setMedia($media);
+      }
+
       $mailers[] = $mailer;
     }
 
@@ -618,6 +624,24 @@
       }
     }
 
+    // Select only the mailers which can transmit messages with requested media
+    // types.
+    if (!empty($constraints['media'])) {
+      foreach ($mailers as $key => $mailer) {
+        $supports_any = false;
+        foreach ($constraints['media'] as $medium) {
+          if ($mailer->supportsMessageType($medium)) {
+            $supports_any = true;
+            break;
+          }
+        }
+
+        if (!$supports_any) {
+          unset($mailers[$key]);
+        }
+      }
+    }
+
     $sorted = array();
     $groups = mgroup($mailers, 'getPriority');
     krsort($groups);
diff --git a/src/applications/metamta/storage/__tests__/PhabricatorMetaMTAMailTestCase.php b/src/applications/metamta/storage/__tests__/PhabricatorMetaMTAMailTestCase.php
--- a/src/applications/metamta/storage/__tests__/PhabricatorMetaMTAMailTestCase.php
+++ b/src/applications/metamta/storage/__tests__/PhabricatorMetaMTAMailTestCase.php
@@ -17,7 +17,7 @@
     $mail = new PhabricatorMetaMTAMail();
     $mail->addTos(array($phid));
 
-    $mailer = new PhabricatorMailImplementationTestAdapter();
+    $mailer = new PhabricatorMailTestAdapter();
     $mail->sendWithMailers(array($mailer));
     $this->assertEqual(
       PhabricatorMailOutboundStatus::STATUS_SENT,
@@ -28,7 +28,7 @@
     $mail = new PhabricatorMetaMTAMail();
     $mail->addTos(array($phid));
 
-    $mailer = new PhabricatorMailImplementationTestAdapter();
+    $mailer = new PhabricatorMailTestAdapter();
     $mailer->setFailTemporarily(true);
     try {
       $mail->sendWithMailers(array($mailer));
@@ -44,7 +44,7 @@
     $mail = new PhabricatorMetaMTAMail();
     $mail->addTos(array($phid));
 
-    $mailer = new PhabricatorMailImplementationTestAdapter();
+    $mailer = new PhabricatorMailTestAdapter();
     $mailer->setFailPermanently(true);
     try {
       $mail->sendWithMailers(array($mailer));
@@ -60,7 +60,7 @@
     $user = $this->generateNewTestUser();
     $phid = $user->getPHID();
 
-    $mailer = new PhabricatorMailImplementationTestAdapter();
+    $mailer = new PhabricatorMailTestAdapter();
 
     $mail = new PhabricatorMetaMTAMail();
     $mail->addTos(array($phid));
@@ -182,7 +182,7 @@
     $supports_message_id,
     $is_first_mail) {
 
-    $mailer = new PhabricatorMailImplementationTestAdapter();
+    $mailer = new PhabricatorMailTestAdapter();
 
     $mailer->prepareForSend(
       array(
@@ -261,10 +261,10 @@
     $status_queue = PhabricatorMailOutboundStatus::STATUS_QUEUE;
     $status_fail = PhabricatorMailOutboundStatus::STATUS_FAIL;
 
-    $mailer1 = id(new PhabricatorMailImplementationTestAdapter())
+    $mailer1 = id(new PhabricatorMailTestAdapter())
       ->setKey('mailer1');
 
-    $mailer2 = id(new PhabricatorMailImplementationTestAdapter())
+    $mailer2 = id(new PhabricatorMailTestAdapter())
       ->setKey('mailer2');
 
     $mailers = array(
@@ -350,7 +350,7 @@
       ->setBody($string_1kb)
       ->setHTMLBody($html_1kb);
 
-    $mailer = new PhabricatorMailImplementationTestAdapter();
+    $mailer = new PhabricatorMailTestAdapter();
     $mail->sendWithMailers(array($mailer));
     $this->assertEqual(
       PhabricatorMailOutboundStatus::STATUS_SENT,
@@ -370,7 +370,7 @@
       ->setBody($string_1mb)
       ->setHTMLBody($html_1mb);
 
-    $mailer = new PhabricatorMailImplementationTestAdapter();
+    $mailer = new PhabricatorMailTestAdapter();
     $mail->sendWithMailers(array($mailer));
     $this->assertEqual(
       PhabricatorMailOutboundStatus::STATUS_SENT,
@@ -398,7 +398,7 @@
       ->setBody($string_1kb)
       ->setHTMLBody($html_1mb);
 
-    $mailer = new PhabricatorMailImplementationTestAdapter();
+    $mailer = new PhabricatorMailTestAdapter();
     $mail->sendWithMailers(array($mailer));
     $this->assertEqual(
       PhabricatorMailOutboundStatus::STATUS_SENT,
diff --git a/src/docs/user/configuration/configuring_outbound_email.diviner b/src/docs/user/configuration/configuring_outbound_email.diviner
--- a/src/docs/user/configuration/configuring_outbound_email.diviner
+++ b/src/docs/user/configuration/configuring_outbound_email.diviner
@@ -85,12 +85,18 @@
     used to receive inbound mail.
   - `outbound`: Optional bool. Use `false` to prevent this mailer from being
     used to send outbound mail.
+  - `media`: Optional list<string>. Some mailers support delivering multiple
+    types of messages (like Email and SMS). If you want to configure a mailer
+    to support only a subset of possible message types, list only those message
+    types. Normally, you do not need to configure this. See below for a list
+    of media types.
 
 The `type` field can be used to select these third-party mailers:
 
   - `mailgun`: Use Mailgun.
   - `ses`: Use Amazon SES.
   - `sendgrid`: Use Sendgrid.
+  - `postmark`: Use Postmark.
 
 It also supports these local mailers:
 
@@ -99,7 +105,11 @@
   - `test`: Internal mailer for testing. Does not send mail.
 
 You can also write your own mailer by extending
-`PhabricatorMailImplementationAdapter`.
+`PhabricatorMailAdapter`.
+
+The `media` field supports these values:
+
+  - `email`: Configure this mailer for email.
 
 Once you've selected a mailer, find the corresponding section below for
 instructions on configuring it.
@@ -171,11 +181,13 @@
 
 ```lang=json
 [
-  "50.31.156.6/32"
+  "50.31.156.6/32",
+  "50.31.156.77/32",
+  "18.217.206.57/32"
 ]
 ```
 
-The default address ranges were last updated in February 2018, and were
+The default address ranges were last updated in January 2019, and were
 documented at: <https://postmarkapp.com/support/article/800-ips-for-firewalls>
 
 
diff --git a/src/infrastructure/cluster/config/PhabricatorClusterMailersConfigType.php b/src/infrastructure/cluster/config/PhabricatorClusterMailersConfigType.php
--- a/src/infrastructure/cluster/config/PhabricatorClusterMailersConfigType.php
+++ b/src/infrastructure/cluster/config/PhabricatorClusterMailersConfigType.php
@@ -31,7 +31,7 @@
       }
     }
 
-    $adapters = PhabricatorMailImplementationAdapter::getAllAdapters();
+    $adapters = PhabricatorMailAdapter::getAllAdapters();
 
     $map = array();
     foreach ($value as $index => $spec) {