diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationAdapter.php
@@ -2,6 +2,9 @@
 
 abstract class PhabricatorMailImplementationAdapter extends Phobject {
 
+  private $key;
+  private $options = array();
+
   abstract public function setFrom($email, $name = '');
   abstract public function addReplyTo($email, $name = '');
   abstract public function addTos(array $emails);
@@ -12,6 +15,7 @@
   abstract public function setHTMLBody($html_body);
   abstract public function setSubject($subject);
 
+
   /**
    * Some mailers, notably Amazon SES, do not support us setting a specific
    * Message-ID header.
@@ -32,4 +36,40 @@
    */
   abstract public function send();
 
+  final public function setKey($key) {
+    $this->key = $key;
+    return $this;
+  }
+
+  final public function getKey() {
+    return $this->key;
+  }
+
+  final public function getOption($key) {
+    if (!array_key_exists($key, $this->options)) {
+      throw new Exception(
+        pht(
+          'Mailer ("%s") is attempting to access unknown option ("%s").',
+          get_class($this),
+          $key));
+    }
+
+    return $this->options[$key];
+  }
+
+  final public function setOptions(array $options) {
+    $this->validateOptions($options);
+    $this->options = $options;
+    return $this;
+  }
+
+  abstract protected function validateOptions(array $options);
+
+  abstract public function newDefaultOptions();
+  abstract public function newLegacyOptions();
+
+  public function prepareForSend() {
+    return;
+  }
+
 }
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php
@@ -6,8 +6,8 @@
   private $message;
   private $isHTML;
 
-  public function __construct() {
-    parent::__construct();
+  public function prepareForSend() {
+    parent::prepareForSend();
     $this->mailer->Mailer = 'amazon-ses';
     $this->mailer->customMailer = $this;
   }
@@ -17,13 +17,39 @@
     return false;
   }
 
+  protected function validateOptions(array $options) {
+    PhutilTypeSpec::checkMap(
+      $options,
+      array(
+        'access-key' => 'string',
+        'secret-key' => 'string',
+        'endpoint' => 'string',
+      ));
+  }
+
+  public function newDefaultOptions() {
+    return array(
+      'access-key' => null,
+      'secret-key' => null,
+      'endpoint' => null,
+    );
+  }
+
+  public function newLegacyOptions() {
+    return array(
+      'access-key' => PhabricatorEnv::getEnvConfig('amazon-ses.access-key'),
+      'secret-key' => PhabricatorEnv::getEnvConfig('amazon-ses.secret-key'),
+      'endpoint' => PhabricatorEnv::getEnvConfig('amazon-ses.endpoint'),
+    );
+  }
+
   /**
    * @phutil-external-symbol class SimpleEmailService
    */
   public function executeSend($body) {
-    $key = PhabricatorEnv::getEnvConfig('amazon-ses.access-key');
-    $secret = PhabricatorEnv::getEnvConfig('amazon-ses.secret-key');
-    $endpoint = PhabricatorEnv::getEnvConfig('amazon-ses.endpoint');
+    $key = $this->getOption('access-key');
+    $secret = $this->getOption('secret-key');
+    $endpoint = $this->getOption('endpoint');
 
     $root = phutil_get_library_root('phabricator');
     $root = dirname($root);
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php
@@ -71,9 +71,32 @@
     return true;
   }
 
+  protected function validateOptions(array $options) {
+    PhutilTypeSpec::checkMap(
+      $options,
+      array(
+        'api-key' => 'string',
+        'domain' => 'string',
+      ));
+  }
+
+  public function newDefaultOptions() {
+    return array(
+      'api-key' => null,
+      'domain' => null,
+    );
+  }
+
+  public function newLegacyOptions() {
+    return array(
+      'api-key' => PhabricatorEnv::getEnvConfig('mailgun.api-key'),
+      'domain' => PhabricatorEnv::getEnvConfig('mailgun.domain'),
+    );
+  }
+
   public function send() {
-    $key = PhabricatorEnv::getEnvConfig('mailgun.api-key');
-    $domain = PhabricatorEnv::getEnvConfig('mailgun.domain');
+    $key = $this->getOption('api-key');
+    $domain = $this->getOption('domain');
     $params = array();
 
     $params['to'] = implode(', ', idx($this->params, 'tos', array()));
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php
@@ -5,17 +5,55 @@
 
   private $mailer;
 
+  protected function validateOptions(array $options) {
+    PhutilTypeSpec::checkMap(
+      $options,
+      array(
+        'host' => 'string|null',
+        'port' => 'int',
+        'user' => 'string|null',
+        'password' => 'string|null',
+        'protocol' => 'string|null',
+        'encoding' => 'string',
+        'mailer' => 'string',
+      ));
+  }
+
+  public function newDefaultOptions() {
+    return array(
+      'host' => null,
+      'port' => 25,
+      'user' => null,
+      'password' => null,
+      'protocol' => null,
+      'encoding' => 'base64',
+      'mailer' => 'smtp',
+    );
+  }
+
+  public function newLegacyOptions() {
+    return array(
+      'host' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-host'),
+      'port' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-port'),
+      'user' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-user'),
+      'password' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-passsword'),
+      'protocol' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-protocol'),
+      'encoding' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-encoding'),
+      'mailer' => PhabricatorEnv::getEnvConfig('phpmailer.mailer'),
+    );
+  }
+
   /**
    * @phutil-external-symbol class PHPMailer
    */
-  public function __construct() {
+  public function prepareForSend() {
     $root = phutil_get_library_root('phabricator');
     $root = dirname($root);
     require_once $root.'/externals/phpmailer/class.phpmailer.php';
     $this->mailer = new PHPMailer($use_exceptions = true);
     $this->mailer->CharSet = 'utf-8';
 
-    $encoding = PhabricatorEnv::getEnvConfig('phpmailer.smtp-encoding');
+    $encoding = $this->getOption('encoding');
     $this->mailer->Encoding = $encoding;
 
     // By default, PHPMailer sends one mail per recipient. We handle
@@ -23,20 +61,19 @@
     // send mail exactly like we ask.
     $this->mailer->SingleTo = false;
 
-    $mailer = PhabricatorEnv::getEnvConfig('phpmailer.mailer');
+    $mailer = $this->getOption('mailer');
     if ($mailer == 'smtp') {
       $this->mailer->IsSMTP();
-      $this->mailer->Host = PhabricatorEnv::getEnvConfig('phpmailer.smtp-host');
-      $this->mailer->Port = PhabricatorEnv::getEnvConfig('phpmailer.smtp-port');
-      $user = PhabricatorEnv::getEnvConfig('phpmailer.smtp-user');
+      $this->mailer->Host = $this->getOption('host');
+      $this->mailer->Port = $this->getOption('port');
+      $user = $this->getOption('user');
       if ($user) {
         $this->mailer->SMTPAuth = true;
         $this->mailer->Username = $user;
-        $this->mailer->Password =
-          PhabricatorEnv::getEnvConfig('phpmailer.smtp-password');
+        $this->mailer->Password = $this->getOption('password');
       }
 
-      $protocol = PhabricatorEnv::getEnvConfig('phpmailer.smtp-protocol');
+      $protocol = $this->getOption('protocol');
       if ($protocol) {
         $protocol = phutil_utf8_strtolower($protocol);
         $this->mailer->SMTPSecure = $protocol;
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php
@@ -8,17 +8,37 @@
 
   protected $mailer;
 
+  protected function validateOptions(array $options) {
+    PhutilTypeSpec::checkMap(
+      $options,
+      array(
+        'encoding' => 'string',
+      ));
+  }
+
+  public function newDefaultOptions() {
+    return array(
+      'encoding' => 'base64',
+    );
+  }
+
+  public function newLegacyOptions() {
+    return array(
+      'encoding' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-encoding'),
+    );
+  }
+
   /**
    * @phutil-external-symbol class PHPMailerLite
    */
-  public function __construct() {
+  public function prepareForSend() {
     $root = phutil_get_library_root('phabricator');
     $root = dirname($root);
     require_once $root.'/externals/phpmailer/class.phpmailer-lite.php';
     $this->mailer = new PHPMailerLite($use_exceptions = true);
     $this->mailer->CharSet = 'utf-8';
 
-    $encoding = PhabricatorEnv::getEnvConfig('phpmailer.smtp-encoding');
+    $encoding = $this->getOption('encoding');
     $this->mailer->Encoding = $encoding;
 
     // By default, PHPMailerLite sends one mail per recipient. We handle
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php
@@ -8,6 +8,29 @@
 
   private $params = array();
 
+  protected function validateOptions(array $options) {
+    PhutilTypeSpec::checkMap(
+      $options,
+      array(
+        'api-user' => 'string',
+        'api-key' => 'string',
+      ));
+  }
+
+  public function newDefaultOptions() {
+    return array(
+      'api-user' => null,
+      'api-key' => null,
+    );
+  }
+
+  public function newLegacyOptions() {
+    return array(
+      'api-user' => PhabricatorEnv::getEnvConfig('sendgrid.api-user'),
+      'api-key' => PhabricatorEnv::getEnvConfig('sendgrid.api-key'),
+    );
+  }
+
   public function setFrom($email, $name = '') {
     $this->params['from'] = $email;
     $this->params['from-name'] = $name;
@@ -73,8 +96,8 @@
 
   public function send() {
 
-    $user = PhabricatorEnv::getEnvConfig('sendgrid.api-user');
-    $key  = PhabricatorEnv::getEnvConfig('sendgrid.api-key');
+    $user = $this->getOption('api-user');
+    $key = $this->getOption('api-key');
 
     if (!$user || !$key) {
       throw new Exception(
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php
--- a/src/applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php
@@ -8,9 +8,23 @@
   extends PhabricatorMailImplementationAdapter {
 
   private $guts = array();
-  private $config;
+  private $config = array();
 
-  public function __construct(array $config = array()) {
+  protected function validateOptions(array $options) {
+    PhutilTypeSpec::checkMap(
+      $options,
+      array());
+  }
+
+  public function newDefaultOptions() {
+    return array();
+  }
+
+  public function newLegacyOptions() {
+    return array();
+  }
+
+  public function prepareForSend(array $config = array()) {
     $this->config = $config;
   }
 
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
@@ -453,11 +453,6 @@
     return $result;
   }
 
-  public function buildDefaultMailer() {
-    return PhabricatorEnv::newObjectFromConfig('metamta.mail-adapter');
-  }
-
-
   /**
    * Attempt to deliver an email immediately, in this process.
    *
@@ -468,13 +463,31 @@
       throw new Exception(pht('Trying to send an already-sent mail!'));
     }
 
-    $mailers = array(
-      $this->buildDefaultMailer(),
-    );
+    $mailers = $this->newMailers();
 
     return $this->sendWithMailers($mailers);
   }
 
+  private function newMailers() {
+    $mailers = array();
+
+    $mailer = PhabricatorEnv::newObjectFromConfig('metamta.mail-adapter');
+
+    $defaults = $mailer->newDefaultOptions();
+    $options = $mailer->newLegacyOptions();
+
+    $options = $options + $defaults;
+
+    $mailer
+      ->setKey('default')
+      ->setOptions($options);
+
+    $mailer->prepareForSend();
+
+    $mailers[] = $mailer;
+
+    return $mailers;
+  }
 
   public function sendWithMailers(array $mailers) {
     $exceptions = array();
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
@@ -182,7 +182,9 @@
     $supports_message_id,
     $is_first_mail) {
 
-    $mailer = new PhabricatorMailImplementationTestAdapter(
+    $mailer = new PhabricatorMailImplementationTestAdapter();
+
+    $mailer->prepareForSend(
       array(
         'supportsMessageIDHeader' => $supports_message_id,
       ));