Refactor mail to produce an intermediate "bag of strings" object in preparation for SMS

Summary:
Depends on D19954. Ref T920. This is a step toward a world where "Mailers" are generic and may send messages over a broader array of channels (email, SMS, postal mail).

There are a few major parts here:

  - Instead of calling `$mailer->setSubject()`, `$mailer->setFrom()`, etc., build in intermediate `$message` object first, then pass that to the mailer.
    - This breaks every mailer! This change on its own does not fix them. I plan to fix them in a series of "update mailer X", "update mailer Y" followups.
    - This generally makes the API easier to change in the far future, and in the near future supports mailers accepting different types of `$message` objects with the same API.
  - Pull the "build an email" stuff out into a `PhabricatorMailEmailEngine`. `MetaMTAMail` is already a huge object without also doing this translation step. This is just a separation/simplification change, but also tries to fight against `MetaMTAMail` getting 5K lines of email/sms/whatsapp/postal-mail code.
  - Try to rewrite the "build an email" stuff to be a bit more straightforward while making it generate objects. Prior to this change, it had this weird flow:

```lang=php
foreach ($properties as $key => $prop) {
  switch ($key) {
    case 'xyz':
      // ...
  }
}
```

This is just inherently somewhat hard to puzzle out, and it means that processing order depends on internal property order, which is quite surprising.

Test Plan: This breaks everything on its own; adapters must be updated to use the new API. See followups.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T920

Differential Revision: https://secure.phabricator.com/D19955

src/__phutil_library_map__.php

@@ -3389,6 +3389,7 @@ phutil_register_library_map(array(
     'PhabricatorMacroViewController' => 'applications/macro/controller/PhabricatorMacroViewController.php',
     'PhabricatorMailAttachment' => 'applications/metamta/message/PhabricatorMailAttachment.php',
     'PhabricatorMailConfigTestCase' => 'applications/metamta/storage/__tests__/PhabricatorMailConfigTestCase.php',
+    'PhabricatorMailEmailEngine' => 'applications/metamta/engine/PhabricatorMailEmailEngine.php',
     'PhabricatorMailEmailHeraldField' => 'applications/metamta/herald/PhabricatorMailEmailHeraldField.php',
     'PhabricatorMailEmailHeraldFieldGroup' => 'applications/metamta/herald/PhabricatorMailEmailHeraldFieldGroup.php',
     'PhabricatorMailEmailMessage' => 'applications/metamta/message/PhabricatorMailEmailMessage.php',
@@ -3414,6 +3415,7 @@ phutil_register_library_map(array(
     'PhabricatorMailManagementUnverifyWorkflow' => 'applications/metamta/management/PhabricatorMailManagementUnverifyWorkflow.php',
     'PhabricatorMailManagementVolumeWorkflow' => 'applications/metamta/management/PhabricatorMailManagementVolumeWorkflow.php',
     'PhabricatorMailManagementWorkflow' => 'applications/metamta/management/PhabricatorMailManagementWorkflow.php',
+    'PhabricatorMailMessageEngine' => 'applications/metamta/engine/PhabricatorMailMessageEngine.php',
     'PhabricatorMailMustEncryptHeraldAction' => 'applications/metamta/herald/PhabricatorMailMustEncryptHeraldAction.php',
     'PhabricatorMailOutboundMailHeraldAdapter' => 'applications/metamta/herald/PhabricatorMailOutboundMailHeraldAdapter.php',
     'PhabricatorMailOutboundRoutingHeraldAction' => 'applications/metamta/herald/PhabricatorMailOutboundRoutingHeraldAction.php',
@@ -9221,6 +9223,7 @@ phutil_register_library_map(array(
     'PhabricatorMacroViewController' => 'PhabricatorMacroController',
     'PhabricatorMailAttachment' => 'Phobject',
     'PhabricatorMailConfigTestCase' => 'PhabricatorTestCase',
+    'PhabricatorMailEmailEngine' => 'PhabricatorMailMessageEngine',
     'PhabricatorMailEmailHeraldField' => 'HeraldField',
     'PhabricatorMailEmailHeraldFieldGroup' => 'HeraldFieldGroup',
     'PhabricatorMailEmailMessage' => 'PhabricatorMailExternalMessage',
@@ -9246,6 +9249,7 @@ phutil_register_library_map(array(
     'PhabricatorMailManagementUnverifyWorkflow' => 'PhabricatorMailManagementWorkflow',
     'PhabricatorMailManagementVolumeWorkflow' => 'PhabricatorMailManagementWorkflow',
     'PhabricatorMailManagementWorkflow' => 'PhabricatorManagementWorkflow',
+    'PhabricatorMailMessageEngine' => 'Phobject',
     'PhabricatorMailMustEncryptHeraldAction' => 'HeraldAction',
     'PhabricatorMailOutboundMailHeraldAdapter' => 'HeraldAdapter',
     'PhabricatorMailOutboundRoutingHeraldAction' => 'HeraldAction',

src/applications/metamta/controller/PhabricatorMetaMTAMailViewController.php

@@ -187,9 +187,6 @@ final class PhabricatorMetaMTAMailViewController
       ->setStacked(true);
 
     $headers = $mail->getDeliveredHeaders();
-    if ($headers === null) {
-      $headers = $mail->generateHeaders();
-    }
 
     // Sort headers by name.
     $headers = isort($headers, 0);

src/applications/metamta/engine/PhabricatorMailEmailEngine.php

@@ -0,0 +1,649 @@
+<?php
+
+final class PhabricatorMailEmailEngine
+  extends PhabricatorMailMessageEngine {
+
+  public function newMessage() {
+    $mailer = $this->getMailer();
+    $mail = $this->getMail();
+
+    $message = new PhabricatorMailEmailMessage();
+
+    $from_address = $this->newFromEmailAddress();
+    $message->setFromAddress($from_address);
+
+    $reply_address = $this->newReplyToEmailAddress();
+    if ($reply_address) {
+      $message->setReplyToAddress($reply_address);
+    }
+
+    $to_addresses = $this->newToEmailAddresses();
+    $cc_addresses = $this->newCCEmailAddresses();
+
+    if (!$to_addresses && !$cc_addresses) {
+      $mail->setMessage(
+        pht(
+          'Message has no valid recipients: all To/CC are disabled, '.
+          'invalid, or configured not to receive this mail.'));
+      return null;
+    }
+
+    // If this email describes a mail processing error, we rate limit outbound
+    // messages to each individual address. This prevents messes where
+    // something is stuck in a loop or dumps a ton of messages on us suddenly.
+    if ($mail->getIsErrorEmail()) {
+      $all_recipients = array();
+      foreach ($to_addresses as $to_address) {
+        $all_recipients[] = $to_address->getAddress();
+      }
+      foreach ($cc_addresses as $cc_address) {
+        $all_recipients[] = $cc_address->getAddress();
+      }
+      if ($this->shouldRateLimitMail($all_recipients)) {
+        $mail->setMessage(
+          pht(
+            'This is an error email, but one or more recipients have '.
+            'exceeded the error email rate limit. Declining to deliver '.
+            'message.'));
+        return null;
+      }
+    }
+
+    // Some mailers require a valid "To:" in order to deliver mail. If we
+    // don't have any "To:", try to fill it in with a placeholder "To:".
+    // If that also fails, move the "Cc:" line to "To:".
+    if (!$to_addresses) {
+      $void_address = $this->newVoidEmailAddress();
+      $cc_addresses = $to_addresses;
+      $to_addresses = array($void_address);
+    }
+
+    $to_addresses = $this->getUniqueEmailAddresses($to_addresses);
+    $cc_addresses = $this->getUniqueEmailAddresses(
+      $cc_addresses,
+      $to_addresses);
+
+    $message->setToAddresses($to_addresses);
+    $message->setCCAddresses($cc_addresses);
+
+    $attachments = $this->newEmailAttachments();
+    $message->setAttachments($attachments);
+
+    $subject = $this->newEmailSubject();
+    $message->setSubject($subject);
+
+    $headers = $this->newEmailHeaders();
+    foreach ($this->newEmailThreadingHeaders($mailer) as $threading_header) {
+      $headers[] = $threading_header;
+    }
+
+    $stamps = $mail->getMailStamps();
+    if ($stamps) {
+      $headers[] = $this->newEmailHeader(
+        'X-Phabricator-Stamps',
+        implode(' ', $stamps));
+    }
+
+    $must_encrypt = $mail->getMustEncrypt();
+
+    $raw_body = $mail->getBody();
+    $body = $raw_body;
+    if ($must_encrypt) {
+      $parts = array();
+
+      $encrypt_uri = $this->getMustEncryptURI();
+      if (!strlen($encrypt_uri)) {
+        $encrypt_phid = $this->getRelatedPHID();
+        if ($encrypt_phid) {
+          $encrypt_uri = urisprintf(
+            '/object/%s/',
+            $encrypt_phid);
+        }
+      }
+
+      if (strlen($encrypt_uri)) {
+        $parts[] = pht(
+          'This secure message is notifying you of a change to this object:');
+        $parts[] = PhabricatorEnv::getProductionURI($encrypt_uri);
+      }
+
+      $parts[] = pht(
+        'The content for this message can only be transmitted over a '.
+        'secure channel. To view the message content, follow this '.
+        'link:');
+
+      $parts[] = PhabricatorEnv::getProductionURI($this->getURI());
+
+      $body = implode("\n\n", $parts);
+    } else {
+      $body = $raw_body;
+    }
+
+    $body_limit = PhabricatorEnv::getEnvConfig('metamta.email-body-limit');
+    if (strlen($body) > $body_limit) {
+      $body = id(new PhutilUTF8StringTruncator())
+        ->setMaximumBytes($body_limit)
+        ->truncateString($body);
+      $body .= "\n";
+      $body .= pht('(This email was truncated at %d bytes.)', $body_limit);
+    }
+    $message->setTextBody($body);
+    $body_limit -= strlen($body);
+
+    // If we sent a different message body than we were asked to, record
+    // what we actually sent to make debugging and diagnostics easier.
+    if ($body !== $raw_body) {
+      $mail->setDeliveredBody($body);
+    }
+
+    if ($must_encrypt) {
+      $send_html = false;
+    } else {
+      $send_html = $this->shouldSendHTML();
+    }
+
+    if ($send_html) {
+      $html_body = $mail->getHTMLBody();
+      if (strlen($html_body)) {
+        // NOTE: We just drop the entire HTML body if it won't fit. Safely
+        // truncating HTML is hard, and we already have the text body to fall
+        // back to.
+        if (strlen($html_body) <= $body_limit) {
+          $message->setHTMLBody($html_body);
+          $body_limit -= strlen($html_body);
+        }
+      }
+    }
+
+    // Pass the headers to the mailer, then save the state so we can show
+    // them in the web UI. If the mail must be encrypted, we remove headers
+    // which are not on a strict whitelist to avoid disclosing information.
+    $filtered_headers = $this->filterHeaders($headers, $must_encrypt);
+    $message->setHeaders($filtered_headers);
+
+    $mail->setUnfilteredHeaders($headers);
+    $mail->setDeliveredHeaders($headers);
+
+    if (PhabricatorEnv::getEnvConfig('phabricator.silent')) {
+      $mail->setMessage(
+        pht(
+          'Phabricator is running in silent mode. See `%s` '.
+          'in the configuration to change this setting.',
+          'phabricator.silent'));
+
+      return null;
+    }
+
+    return $message;
+  }
+
+/* -(  Message Components  )------------------------------------------------- */
+
+  private function newFromEmailAddress() {
+    $from_address = $this->newDefaultEmailAddress();
+    $mail = $this->getMail();
+
+    // If the mail content must be encrypted, always disguise the sender.
+    $must_encrypt = $mail->getMustEncrypt();
+    if ($must_encrypt) {
+      return $from_address;
+    }
+
+    // If we have a raw "From" address, use that.
+    $raw_from = $mail->getRawFrom();
+    if ($raw_from) {
+      list($from_email, $from_name) = $raw_from;
+      return $this->newEmailAddress($from_email, $from_name);
+    }
+
+    // Otherwise, use as much of the information for any sending entity as
+    // we can.
+    $from_phid = $mail->getFrom();
+
+    $actor = $this->getActor($from_phid);
+    if ($actor) {
+      $actor_email = $actor->getEmailAddress();
+      $actor_name = $actor->getName();
+    } else {
+      $actor_email = null;
+      $actor_name = null;
+    }
+
+    $send_as_user = PhabricatorEnv::getEnvConfig('metamta.can-send-as-user');
+    if ($send_as_user) {
+      if ($actor_email !== null) {
+        $from_address->setAddress($actor_email);
+      }
+    }
+
+    if ($actor_name !== null) {
+      $from_address->setDisplayName($actor_name);
+    }
+
+    return $from_address;
+  }
+
+  private function newReplyToEmailAddress() {
+    $mail = $this->getMail();
+
+    $reply_raw = $mail->getReplyTo();
+    if (!strlen($reply_raw)) {
+      return null;
+    }
+
+    $reply_address = new PhutilEmailAddress($reply_raw);
+
+    // If we have a sending object, change the display name.
+    $from_phid = $mail->getFrom();
+    $actor = $this->getActor($from_phid);
+    if ($actor) {
+      $reply_address->setDisplayName($actor->getName());
+    }
+
+    // If we don't have a display name, fill in a default.
+    if (!strlen($reply_address->getDisplayName())) {
+      $reply_address->setDisplayName(pht('Phabricator'));
+    }
+
+    return $reply_address;
+  }
+
+  private function newToEmailAddresses() {
+    $mail = $this->getMail();
+
+    $phids = $mail->getToPHIDs();
+    $addresses = $this->newEmailAddressesFromActorPHIDs($phids);
+
+    foreach ($mail->getRawToAddresses() as $raw_address) {
+      $addresses[] = new PhutilEmailAddress($raw_address);
+    }
+
+    return $addresses;
+  }
+
+  private function newCCEmailAddresses() {
+    $mail = $this->getMail();
+    $phids = $mail->getCcPHIDs();
+    return $this->newEmailAddressesFromActorPHIDs($phids);
+  }
+
+  private function newEmailAddressesFromActorPHIDs(array $phids) {
+    $mail = $this->getMail();
+    $phids = $mail->expandRecipients($phids);
+
+    $addresses = array();
+    foreach ($phids as $phid) {
+      $actor = $this->getActor($phid);
+      if (!$actor) {
+        continue;
+      }
+
+      if (!$actor->isDeliverable()) {
+        continue;
+      }
+
+      $addresses[] = new PhutilEmailAddress($actor->getEmailAddress());
+    }
+
+    return $addresses;
+  }
+
+  private function newEmailSubject() {
+    $mail = $this->getMail();
+
+    $is_threaded = (bool)$mail->getThreadID();
+    $must_encrypt = $mail->getMustEncrypt();
+
+    $subject = array();
+
+    if ($is_threaded) {
+      if ($this->shouldAddRePrefix()) {
+        $subject[] = 'Re:';
+      }
+    }
+
+    $subject[] = trim($mail->getSubjectPrefix());
+
+    // If mail content must be encrypted, we replace the subject with
+    // a generic one.
+    if ($must_encrypt) {
+      $encrypt_subject = $mail->getMustEncryptSubject();
+      if (!strlen($encrypt_subject)) {
+        $encrypt_subject = pht('Object Updated');
+      }
+      $subject[] = $encrypt_subject;
+    } else {
+      $vary_prefix = $mail->getVarySubjectPrefix();
+      if (strlen($vary_prefix)) {
+        if ($this->shouldVarySubject()) {
+          $subject[] = $vary_prefix;
+        }
+      }
+
+      $subject[] = $mail->getSubject();
+    }
+
+    foreach ($subject as $key => $part) {
+      if (!strlen($part)) {
+        unset($subject[$key]);
+      }
+    }
+
+    $subject = implode(' ', $subject);
+    return $subject;
+  }
+
+  private function newEmailHeaders() {
+    $mail = $this->getMail();
+
+    $headers = array();
+
+    $headers[] = $this->newEmailHeader(
+      'X-Phabricator-Sent-This-Message',
+      'Yes');
+    $headers[] = $this->newEmailHeader(
+      'X-Mail-Transport-Agent',
+      'MetaMTA');
+
+    // Some clients respect this to suppress OOF and other auto-responses.
+    $headers[] = $this->newEmailHeader(
+      'X-Auto-Response-Suppress',
+      'All');
+
+    $mailtags = $mail->getMailTags();
+    if ($mailtags) {
+      $tag_header = array();
+      foreach ($mailtags as $mailtag) {
+        $tag_header[] = '<'.$mailtag.'>';
+      }
+      $tag_header = implode(', ', $tag_header);
+      $headers[] = $this->newEmailHeader(
+        'X-Phabricator-Mail-Tags',
+        $tag_header);
+    }
+
+    $value = $mail->getHeaders();
+    foreach ($value as $pair) {
+      list($header_key, $header_value) = $pair;
+
+      // NOTE: If we have \n in a header, SES rejects the email.
+      $header_value = str_replace("\n", ' ', $header_value);
+      $headers[] = $this->newEmailHeader($header_key, $header_value);
+    }
+
+    $is_bulk = $mail->getIsBulk();
+    if ($is_bulk) {
+      $headers[] = $this->newEmailHeader('Precedence', 'bulk');
+    }
+
+    if ($mail->getMustEncrypt()) {
+      $headers[] = $this->newEmailHeader('X-Phabricator-Must-Encrypt', 'Yes');
+    }
+
+    $related_phid = $mail->getRelatedPHID();
+    if ($related_phid) {
+      $headers[] = $this->newEmailHeader('Thread-Topic', $related_phid);
+    }
+
+    $headers[] = $this->newEmailHeader(
+      'X-Phabricator-Mail-ID',
+      $mail->getID());
+
+    $unique = Filesystem::readRandomCharacters(16);
+    $headers[] = $this->newEmailHeader(
+      'X-Phabricator-Send-Attempt',
+      $unique);
+
+    return $headers;
+  }
+
+  private function newEmailThreadingHeaders() {
+    $mailer = $this->getMailer();
+    $mail = $this->getMail();
+
+    $headers = array();
+
+    $thread_id = $mail->getThreadID();
+    if (!strlen($thread_id)) {
+      return $headers;
+    }
+
+    $is_first = $mail->getIsFirstMessage();
+
+    // NOTE: Gmail freaks out about In-Reply-To and References which aren't in
+    // the form "<string@domain.tld>"; this is also required by RFC 2822,
+    // although some clients are more liberal in what they accept.
+    $domain = $this->newMailDomain();
+    $thread_id = '<'.$thread_id.'@'.$domain.'>';
+
+    if ($is_first && $mailer->supportsMessageIDHeader()) {
+      $headers[] = $this->newEmailHeader('Message-ID',  $thread_id);
+    } else {
+      $in_reply_to = $thread_id;
+      $references = array($thread_id);
+      $parent_id = $mail->getParentMessageID();
+      if ($parent_id) {
+        $in_reply_to = $parent_id;
+        // By RFC 2822, the most immediate parent should appear last
+        // in the "References" header, so this order is intentional.
+        $references[] = $parent_id;
+      }
+      $references = implode(' ', $references);
+      $headers[] = $this->newEmailHeader('In-Reply-To', $in_reply_to);
+      $headers[] = $this->newEmailHeader('References',  $references);
+    }
+    $thread_index = $this->generateThreadIndex($thread_id, $is_first);
+    $headers[] = $this->newEmailHeader('Thread-Index', $thread_index);
+
+    return $headers;
+  }
+
+  private function newEmailAttachments() {
+    $mail = $this->getMail();
+
+    // If the mail content must be encrypted, don't add attachments.
+    $must_encrypt = $mail->getMustEncrypt();
+    if ($must_encrypt) {
+      return array();
+    }
+
+    return $mail->getAttachments();
+  }
+
+/* -(  Preferences  )-------------------------------------------------------- */
+
+  private function shouldAddRePrefix() {
+    $preferences = $this->getPreferences();
+
+    $value = $preferences->getSettingValue(
+      PhabricatorEmailRePrefixSetting::SETTINGKEY);
+
+    return ($value == PhabricatorEmailRePrefixSetting::VALUE_RE_PREFIX);
+  }
+
+  private function shouldVarySubject() {
+    $preferences = $this->getPreferences();
+
+    $value = $preferences->getSettingValue(
+      PhabricatorEmailVarySubjectsSetting::SETTINGKEY);
+
+    return ($value == PhabricatorEmailVarySubjectsSetting::VALUE_VARY_SUBJECTS);
+  }
+
+  private function shouldSendHTML() {
+    $preferences = $this->getPreferences();
+
+    $value = $preferences->getSettingValue(
+      PhabricatorEmailFormatSetting::SETTINGKEY);
+
+    return ($value == PhabricatorEmailFormatSetting::VALUE_HTML_EMAIL);
+  }
+
+
+/* -(  Utilities  )---------------------------------------------------------- */
+
+  private function newEmailHeader($name, $value) {
+    return id(new PhabricatorMailHeader())
+      ->setName($name)
+      ->setValue($value);
+  }
+
+  private function newEmailAddress($address, $name = null) {
+    $object = id(new PhutilEmailAddress())
+      ->setAddress($address);
+
+    if (strlen($name)) {
+      $object->setDisplayName($name);
+    }
+
+    return $object;
+  }
+
+  public function newDefaultEmailAddress() {
+    $raw_address = PhabricatorEnv::getEnvConfig('metamta.default-address');
+
+    if (!strlen($raw_address)) {
+      $domain = $this->newMailDomain();
+      $raw_address = "noreply@{$domain}";
+    }
+
+    $address = new PhutilEmailAddress($raw_address);
+
+    if (!strlen($address->getDisplayName())) {
+      $address->setDisplayName(pht('Phabricator'));
+    }
+
+    return $address;
+  }
+
+  public function newVoidEmailAddress() {
+    return $this->newDefaultEmailAddress();
+  }
+
+  private function newMailDomain() {
+    $domain = PhabricatorEnv::getEnvConfig('metamta.reply-handler-domain');
+    if (strlen($domain)) {
+      return $domain;
+    }
+
+    $install_uri = PhabricatorEnv::getURI('/');
+    $install_uri = new PhutilURI($install_uri);
+
+    return $install_uri->getDomain();
+  }
+
+  private function filterHeaders(array $headers, $must_encrypt) {
+    assert_instances_of($headers, 'PhabricatorMailHeader');
+
+    if (!$must_encrypt) {
+      return $headers;
+    }
+
+    $whitelist = array(
+      'In-Reply-To',
+      'Message-ID',
+      'Precedence',
+      'References',
+      'Thread-Index',
+      'Thread-Topic',
+
+      'X-Mail-Transport-Agent',
+      'X-Auto-Response-Suppress',
+
+      'X-Phabricator-Sent-This-Message',
+      'X-Phabricator-Must-Encrypt',
+      'X-Phabricator-Mail-ID',
+      'X-Phabricator-Send-Attempt',
+    );
+
+    // NOTE: The major header we want to drop is "X-Phabricator-Mail-Tags".
+    // This header contains a significant amount of meaningful information
+    // about the object.
+
+    $whitelist_map = array();
+    foreach ($whitelist as $term) {
+      $whitelist_map[phutil_utf8_strtolower($term)] = true;
+    }
+
+    foreach ($headers as $key => $header) {
+      $name = $header->getName();
+      $name = phutil_utf8_strtolower($name);
+
+      if (!isset($whitelist_map[$name])) {
+        unset($headers[$key]);
+      }
+    }
+
+    return $headers;
+  }
+
+  private function getUniqueEmailAddresses(
+    array $addresses,
+    array $exclude = array()) {
+    assert_instances_of($addresses, 'PhutilEmailAddress');
+    assert_instances_of($exclude, 'PhutilEmailAddress');
+
+    $seen = array();
+
+    foreach ($exclude as $address) {
+      $seen[$address->getAddress()] = true;
+    }
+
+    foreach ($addresses as $key => $address) {
+      $raw_address = $address->getAddress();
+
+      if (isset($seen[$raw_address])) {
+        unset($addresses[$key]);
+        continue;
+      }
+
+      $seen[$raw_address] = true;
+    }
+
+    return array_values($addresses);
+  }
+
+  private function generateThreadIndex($seed, $is_first_mail) {
+    // When threading, Outlook ignores the 'References' and 'In-Reply-To'
+    // headers that most clients use. Instead, it uses a custom 'Thread-Index'
+    // header. The format of this header is something like this (from
+    // camel-exchange-folder.c in Evolution Exchange):
+
+    /* A new post to a folder gets a 27-byte-long thread index. (The value
+     * is apparently unique but meaningless.) Each reply to a post gets a
+     * 32-byte-long thread index whose first 27 bytes are the same as the
+     * parent's thread index. Each reply to any of those gets a
+     * 37-byte-long thread index, etc. The Thread-Index header contains a
+     * base64 representation of this value.
+     */
+
+    // The specific implementation uses a 27-byte header for the first email
+    // a recipient receives, and a random 5-byte suffix (32 bytes total)
+    // thereafter. This means that all the replies are (incorrectly) siblings,
+    // but it would be very difficult to keep track of the entire tree and this
+    // gets us reasonable client behavior.
+
+    $base = substr(md5($seed), 0, 27);
+    if (!$is_first_mail) {
+      // Not totally sure, but it seems like outlook orders replies by
+      // thread-index rather than timestamp, so to get these to show up in the
+      // right order we use the time as the last 4 bytes.
+      $base .= ' '.pack('N', time());
+    }
+
+    return base64_encode($base);
+  }
+
+  private function shouldRateLimitMail(array $all_recipients) {
+    try {
+      PhabricatorSystemActionEngine::willTakeAction(
+        $all_recipients,
+        new PhabricatorMetaMTAErrorMailAction(),
+        1);
+      return false;
+    } catch (PhabricatorSystemActionRateLimitException $ex) {
+      return true;
+    }
+  }
+
+}

src/applications/metamta/engine/PhabricatorMailMessageEngine.php

@@ -0,0 +1,55 @@
+<?php
+
+abstract class PhabricatorMailMessageEngine
+  extends Phobject {
+
+  private $mailer;
+  private $mail;
+  private $actors = array();
+  private $preferences;
+
+  final public function setMailer(
+    PhabricatorMailImplementationAdapter $mailer) {
+
+    $this->mailer = $mailer;
+    return $this;
+  }
+
+  final public function getMailer() {
+    return $this->mailer;
+  }
+
+  final public function setMail(PhabricatorMetaMTAMail $mail) {
+    $this->mail = $mail;
+    return $this;
+  }
+
+  final public function getMail() {
+    return $this->mail;
+  }
+
+  final public function setActors(array $actors) {
+    assert_instances_of($actors, 'PhabricatorMetaMTAActor');
+    $this->actors = $actors;
+    return $this;
+  }
+
+  final public function getActors() {
+    return $this->actors;
+  }
+
+  final public function getActor($phid) {
+    return idx($this->actors, $phid);
+  }
+
+  final public function setPreferences(
+    PhabricatorUserPreferences $preferences) {
+    $this->preferences = $preferences;
+    return $this;
+  }
+
+  final public function getPreferences() {
+    return $this->preferences;
+  }
+
+}

src/applications/metamta/management/PhabricatorMailManagementShowOutboundWorkflow.php

@@ -116,10 +116,6 @@ final class PhabricatorMailManagementShowOutboundWorkflow
 
       $headers = $message->getDeliveredHeaders();
       $unfiltered = $message->getUnfilteredHeaders();
-      if (!$unfiltered) {
-        $headers = $message->generateHeaders();
-        $unfiltered = $headers;
-      }
 
       $header_map = array();
       foreach ($headers as $header) {

src/applications/metamta/storage/PhabricatorMetaMTAMail.php

@@ -191,13 +191,17 @@ final class PhabricatorMetaMTAMail
     return $this;
   }
 
+  public function getHeaders() {
+    return $this->getParam('headers', array());
+  }
+
   public function addAttachment(PhabricatorMailAttachment $attachment) {
     $this->parameters['attachments'][] = $attachment->toDictionary();
     return $this;
   }
 
   public function getAttachments() {
-    $dicts = $this->getParam('attachments');
+    $dicts = $this->getParam('attachments', array());
 
     $result = array();
     foreach ($dicts as $dict) {
@@ -256,11 +260,19 @@ final class PhabricatorMetaMTAMail
     return $this;
   }
 
+  public function getRawFrom() {
+    return $this->getParam('raw-from');
+  }
+
   public function setReplyTo($reply_to) {
     $this->setParam('reply-to', $reply_to);
     return $this;
   }
 
+  public function getReplyTo() {
+    return $this->getParam('reply-to');
+  }
+
   public function setSubject($subject) {
     $this->setParam('subject', $subject);
     return $this;
@@ -271,11 +283,19 @@ final class PhabricatorMetaMTAMail
     return $this;
   }
 
+  public function getSubjectPrefix() {
+    return $this->getParam('subject-prefix');
+  }
+
   public function setVarySubjectPrefix($prefix) {
     $this->setParam('vary-subject-prefix', $prefix);
     return $this;
   }
 
+  public function getVarySubjectPrefix() {
+    return $this->getParam('vary-subject-prefix');
+  }
+
   public function setBody($body) {
     $this->setParam('body', $body);
     return $this;
@@ -413,6 +433,10 @@ final class PhabricatorMetaMTAMail
     return $this;
   }
 
+  public function getIsBulk() {
+    return $this->getParam('is-bulk');
+  }
+
   /**
    * Use this method to set an ID used for message threading. MetaMTA will
    * set appropriate headers (Message-ID, In-Reply-To, References and
@@ -429,6 +453,14 @@ final class PhabricatorMetaMTAMail
     return $this;
   }
 
+  public function getThreadID() {
+    return $this->getParam('thread-id');
+  }
+
+  public function getIsFirstMessage() {
+    return (bool)$this->getParam('is-first-message');
+  }
+
   /**
    * Save a newly created mail to the database. The mail will eventually be
    * delivered by the MetaMTA daemon.
@@ -597,10 +629,6 @@ final class PhabricatorMetaMTAMail
       }
     }
 
-    foreach ($sorted as $mailer) {
-      $mailer->prepareForSend();
-    }
-
     return $sorted;
   }
 
@@ -627,36 +655,51 @@ final class PhabricatorMetaMTAMail
         ->save();
     }
 
-    $exceptions = array();
+    $actors = $this->loadAllActors();
-    foreach ($mailers as $template_mailer) {
-      $mailer = null;
 
+    // If we're sending one mail to everyone, some recipients will be in
+    // "Cc" rather than "To". We'll move them to "To" later (or supply a
+    // dummy "To") but need to look for the recipient in either the
+    // "To" or "Cc" fields here.
+    $target_phid = head($this->getToPHIDs());
+    if (!$target_phid) {
+      $target_phid = head($this->getCcPHIDs());
+    }
+    $preferences = $this->loadPreferences($target_phid);
+
+    // Attach any files we're about to send to this message, so the recipients
+    // can view them.
+    $viewer = PhabricatorUser::getOmnipotentUser();
+    $files = $this->loadAttachedFiles($viewer);
+    foreach ($files as $file) {
+      $file->attachToObject($this->getPHID());
+    }
+
+    $exceptions = array();
+    foreach ($mailers as $mailer) {
       try {
-        $mailer = $this->buildMailer($template_mailer);
+        $message = id(new PhabricatorMailEmailEngine())
+          ->setMailer($mailer)
+          ->setMail($this)
+          ->setActors($actors)
+          ->setPreferences($preferences)
+          ->newMessage($mailer);
       } catch (Exception $ex) {
         $exceptions[] = $ex;
         continue;
       }
 
-      if (!$mailer) {
+      if (!$message) {
-        // If we don't get a mailer back, that means the mail doesn't
+        // If we don't get a message back, that means the mail doesn't actually
-        // actually need to be sent (for example, because recipients have
+        // need to be sent (for example, because recipients have declined to
-        // declined to receive the mail). Void it and return.
+        // receive the mail). Void it and return.
         return $this
           ->setStatus(PhabricatorMailOutboundStatus::STATUS_VOID)
           ->save();
       }
 
       try {
-        $ok = $mailer->send();
+        $mailer->sendMessage($message);
-        if (!$ok) {
-          // TODO: At some point, we should clean this up and make all mailers
-          // throw.
-          throw new Exception(
-            pht(
-              'Mail adapter encountered an unexpected, unspecified '.
-              'failure.'));
-        }
       } catch (PhabricatorMetaMTAPermanentFailureException $ex) {
         // If any mailer raises a permanent failure, stop trying to send the
         // mail with other mailers.
@@ -677,6 +720,19 @@ final class PhabricatorMetaMTAMail
         $this->setParam('mailer.key', $mailer_key);
       }
 
+      // Now that we sent the message, store the final deliverability outcomes
+      // and reasoning so we can explain why things happened the way they did.
+      $actor_list = array();
+      foreach ($actors as $actor) {
+        $actor_list[$actor->getPHID()] = array(
+          'deliverable' => $actor->isDeliverable(),
+          'reasons' => $actor->getDeliverabilityReasons(),
+        );
+      }
+      $this->setParam('actors.sent', $actor_list);
+      $this->setParam('routing.sent', $this->getParam('routing'));
+      $this->setParam('routingmap.sent', $this->getRoutingRuleMap());
+
       return $this
         ->setStatus(PhabricatorMailOutboundStatus::STATUS_SENT)
         ->save();
@@ -705,368 +761,6 @@ final class PhabricatorMetaMTAMail
       $exceptions);
   }
 
-  private function buildMailer(PhabricatorMailImplementationAdapter $mailer) {
-    $headers = $this->generateHeaders();
-
-    $params = $this->parameters;
-
-    $actors = $this->loadAllActors();
-    $deliverable_actors = $this->filterDeliverableActors($actors);
-
-    $default_from = (string)$this->newDefaultEmailAddress();
-    if (empty($params['from'])) {
-      $mailer->setFrom($default_from);
-    }
-
-    $is_first = idx($params, 'is-first-message');
-    unset($params['is-first-message']);
-
-    $is_threaded = (bool)idx($params, 'thread-id');
-    $must_encrypt = $this->getMustEncrypt();
-
-    $reply_to_name = idx($params, 'reply-to-name', '');
-    unset($params['reply-to-name']);
-
-    $add_cc = array();
-    $add_to = array();
-
-    // If we're sending one mail to everyone, some recipients will be in
-    // "Cc" rather than "To". We'll move them to "To" later (or supply a
-    // dummy "To") but need to look for the recipient in either the
-    // "To" or "Cc" fields here.
-    $target_phid = head(idx($params, 'to', array()));
-    if (!$target_phid) {
-      $target_phid = head(idx($params, 'cc', array()));
-    }
-
-    $preferences = $this->loadPreferences($target_phid);
-
-    foreach ($params as $key => $value) {
-      switch ($key) {
-        case 'raw-from':
-          list($from_email, $from_name) = $value;
-          $mailer->setFrom($from_email, $from_name);
-          break;
-        case 'from':
-          // If the mail content must be encrypted, disguise the sender.
-          if ($must_encrypt) {
-            $mailer->setFrom($default_from, pht('Phabricator'));
-            break;
-          }
-
-          $from = $value;
-          $actor_email = null;
-          $actor_name = null;
-          $actor = idx($actors, $from);
-          if ($actor) {
-            $actor_email = $actor->getEmailAddress();
-            $actor_name = $actor->getName();
-          }
-          $can_send_as_user = $actor_email &&
-            PhabricatorEnv::getEnvConfig('metamta.can-send-as-user');
-
-          if ($can_send_as_user) {
-            $mailer->setFrom($actor_email, $actor_name);
-          } else {
-            $from_email = coalesce($actor_email, $default_from);
-            $from_name = coalesce($actor_name, pht('Phabricator'));
-
-            if (empty($params['reply-to'])) {
-              $params['reply-to'] = $from_email;
-              $params['reply-to-name'] = $from_name;
-            }
-
-            $mailer->setFrom($default_from, $from_name);
-          }
-          break;
-        case 'reply-to':
-          $mailer->addReplyTo($value, $reply_to_name);
-          break;
-        case 'to':
-          $to_phids = $this->expandRecipients($value);
-          $to_actors = array_select_keys($deliverable_actors, $to_phids);
-          $add_to = array_merge(
-            $add_to,
-            mpull($to_actors, 'getEmailAddress'));
-          break;
-        case 'raw-to':
-          $add_to = array_merge($add_to, $value);
-          break;
-        case 'cc':
-          $cc_phids = $this->expandRecipients($value);
-          $cc_actors = array_select_keys($deliverable_actors, $cc_phids);
-          $add_cc = array_merge(
-            $add_cc,
-            mpull($cc_actors, 'getEmailAddress'));
-          break;
-        case 'attachments':
-          $attached_viewer = PhabricatorUser::getOmnipotentUser();
-          $files = $this->loadAttachedFiles($attached_viewer);
-          foreach ($files as $file) {
-            $file->attachToObject($this->getPHID());
-          }
-
-          // If the mail content must be encrypted, don't add attachments.
-          if ($must_encrypt) {
-            break;
-          }
-
-          $value = $this->getAttachments();
-          foreach ($value as $attachment) {
-            $mailer->addAttachment(
-              $attachment->getData(),
-              $attachment->getFilename(),
-              $attachment->getMimeType());
-          }
-          break;
-        case 'subject':
-          $subject = array();
-
-          if ($is_threaded) {
-            if ($this->shouldAddRePrefix($preferences)) {
-              $subject[] = 'Re:';
-            }
-          }
-
-          $subject[] = trim(idx($params, 'subject-prefix'));
-
-          // If mail content must be encrypted, we replace the subject with
-          // a generic one.
-          if ($must_encrypt) {
-            $encrypt_subject = $this->getMustEncryptSubject();
-            if (!strlen($encrypt_subject)) {
-              $encrypt_subject = pht('Object Updated');
-            }
-            $subject[] = $encrypt_subject;
-          } else {
-            $vary_prefix = idx($params, 'vary-subject-prefix');
-            if ($vary_prefix != '') {
-              if ($this->shouldVarySubject($preferences)) {
-                $subject[] = $vary_prefix;
-              }
-            }
-
-            $subject[] = $value;
-          }
-
-          $mailer->setSubject(implode(' ', array_filter($subject)));
-          break;
-        case 'thread-id':
-
-          // NOTE: Gmail freaks out about In-Reply-To and References which
-          // aren't in the form "<string@domain.tld>"; this is also required
-          // by RFC 2822, although some clients are more liberal in what they
-          // accept.
-          $domain = $this->newMailDomain();
-          $value = '<'.$value.'@'.$domain.'>';
-
-          if ($is_first && $mailer->supportsMessageIDHeader()) {
-            $headers[] = array('Message-ID',  $value);
-          } else {
-            $in_reply_to = $value;
-            $references = array($value);
-            $parent_id = $this->getParentMessageID();
-            if ($parent_id) {
-              $in_reply_to = $parent_id;
-              // By RFC 2822, the most immediate parent should appear last
-              // in the "References" header, so this order is intentional.
-              $references[] = $parent_id;
-            }
-            $references = implode(' ', $references);
-            $headers[] = array('In-Reply-To', $in_reply_to);
-            $headers[] = array('References',  $references);
-          }
-          $thread_index = $this->generateThreadIndex($value, $is_first);
-          $headers[] = array('Thread-Index', $thread_index);
-          break;
-        default:
-          // Other parameters are handled elsewhere or are not relevant to
-          // constructing the message.
-          break;
-      }
-    }
-
-    $stamps = $this->getMailStamps();
-    if ($stamps) {
-      $headers[] = array('X-Phabricator-Stamps', implode(' ', $stamps));
-    }
-
-    $raw_body = idx($params, 'body', '');
-    $body = $raw_body;
-    if ($must_encrypt) {
-      $parts = array();
-
-      $encrypt_uri = $this->getMustEncryptURI();
-      if (!strlen($encrypt_uri)) {
-        $encrypt_phid = $this->getRelatedPHID();
-        if ($encrypt_phid) {
-          $encrypt_uri = urisprintf(
-            '/object/%s/',
-            $encrypt_phid);
-        }
-      }
-
-      if (strlen($encrypt_uri)) {
-        $parts[] = pht(
-          'This secure message is notifying you of a change to this object:');
-        $parts[] = PhabricatorEnv::getProductionURI($encrypt_uri);
-      }
-
-      $parts[] = pht(
-        'The content for this message can only be transmitted over a '.
-        'secure channel. To view the message content, follow this '.
-        'link:');
-
-      $parts[] = PhabricatorEnv::getProductionURI($this->getURI());
-
-      $body = implode("\n\n", $parts);
-    } else {
-      $body = $raw_body;
-    }
-
-    $body_limit = PhabricatorEnv::getEnvConfig('metamta.email-body-limit');
-    if (strlen($body) > $body_limit) {
-      $body = id(new PhutilUTF8StringTruncator())
-        ->setMaximumBytes($body_limit)
-        ->truncateString($body);
-      $body .= "\n";
-      $body .= pht('(This email was truncated at %d bytes.)', $body_limit);
-    }
-    $mailer->setBody($body);
-    $body_limit -= strlen($body);
-
-    // If we sent a different message body than we were asked to, record
-    // what we actually sent to make debugging and diagnostics easier.
-    if ($body !== $raw_body) {
-      $this->setParam('body.sent', $body);
-    }
-
-    if ($must_encrypt) {
-      $send_html = false;
-    } else {
-      $send_html = $this->shouldSendHTML($preferences);
-    }
-
-    if ($send_html) {
-      $html_body = idx($params, 'html-body');
-      if (strlen($html_body)) {
-        // NOTE: We just drop the entire HTML body if it won't fit. Safely
-        // truncating HTML is hard, and we already have the text body to fall
-        // back to.
-        if (strlen($html_body) <= $body_limit) {
-          $mailer->setHTMLBody($html_body);
-          $body_limit -= strlen($html_body);
-        }
-      }
-    }
-
-    // Pass the headers to the mailer, then save the state so we can show
-    // them in the web UI. If the mail must be encrypted, we remove headers
-    // which are not on a strict whitelist to avoid disclosing information.
-    $filtered_headers = $this->filterHeaders($headers, $must_encrypt);
-    foreach ($filtered_headers as $header) {
-      list($header_key, $header_value) = $header;
-      $mailer->addHeader($header_key, $header_value);
-    }
-    $this->setParam('headers.unfiltered', $headers);
-    $this->setParam('headers.sent', $filtered_headers);
-
-    // Save the final deliverability outcomes and reasoning so we can
-    // explain why things happened the way they did.
-    $actor_list = array();
-    foreach ($actors as $actor) {
-      $actor_list[$actor->getPHID()] = array(
-        'deliverable' => $actor->isDeliverable(),
-        'reasons' => $actor->getDeliverabilityReasons(),
-      );
-    }
-    $this->setParam('actors.sent', $actor_list);
-
-    $this->setParam('routing.sent', $this->getParam('routing'));
-    $this->setParam('routingmap.sent', $this->getRoutingRuleMap());
-
-    if (!$add_to && !$add_cc) {
-      $this->setMessage(
-        pht(
-          'Message has no valid recipients: all To/Cc are disabled, '.
-          'invalid, or configured not to receive this mail.'));
-
-      return null;
-    }
-
-    if ($this->getIsErrorEmail()) {
-      $all_recipients = array_merge($add_to, $add_cc);
-      if ($this->shouldRateLimitMail($all_recipients)) {
-        $this->setMessage(
-          pht(
-            'This is an error email, but one or more recipients have '.
-            'exceeded the error email rate limit. Declining to deliver '.
-            'message.'));
-
-        return null;
-      }
-    }
-
-    if (PhabricatorEnv::getEnvConfig('phabricator.silent')) {
-      $this->setMessage(
-        pht(
-          'Phabricator is running in silent mode. See `%s` '.
-          'in the configuration to change this setting.',
-          'phabricator.silent'));
-
-      return null;
-    }
-
-    // Some mailers require a valid "To:" in order to deliver mail. If we don't
-    // have any "To:", fill it in with a placeholder "To:". This allows client
-    // rules based on whether the recipient is in "To:" or "CC:" to continue
-    // behaving in the same way.
-    if (!$add_to) {
-      $void_recipient = $this->newVoidEmailAddress();
-      $add_to = array($void_recipient->getAddress());
-    }
-
-    $add_to = array_unique($add_to);
-    $add_cc = array_diff(array_unique($add_cc), $add_to);
-
-    $mailer->addTos($add_to);
-    if ($add_cc) {
-      $mailer->addCCs($add_cc);
-    }
-
-    return $mailer;
-  }
-
-  private function generateThreadIndex($seed, $is_first_mail) {
-    // When threading, Outlook ignores the 'References' and 'In-Reply-To'
-    // headers that most clients use. Instead, it uses a custom 'Thread-Index'
-    // header. The format of this header is something like this (from
-    // camel-exchange-folder.c in Evolution Exchange):
-
-    /* A new post to a folder gets a 27-byte-long thread index. (The value
-     * is apparently unique but meaningless.) Each reply to a post gets a
-     * 32-byte-long thread index whose first 27 bytes are the same as the
-     * parent's thread index. Each reply to any of those gets a
-     * 37-byte-long thread index, etc. The Thread-Index header contains a
-     * base64 representation of this value.
-     */
-
-    // The specific implementation uses a 27-byte header for the first email
-    // a recipient receives, and a random 5-byte suffix (32 bytes total)
-    // thereafter. This means that all the replies are (incorrectly) siblings,
-    // but it would be very difficult to keep track of the entire tree and this
-    // gets us reasonable client behavior.
-
-    $base = substr(md5($seed), 0, 27);
-    if (!$is_first_mail) {
-      // Not totally sure, but it seems like outlook orders replies by
-      // thread-index rather than timestamp, so to get these to show up in the
-      // right order we use the time as the last 4 bytes.
-      $base .= ' '.pack('N', time());
-    }
-
-    return base64_encode($base);
-  }
 
   public static function shouldMailEachRecipient() {
     return PhabricatorEnv::getEnvConfig('metamta.one-mail-per-recipient');
@@ -1120,7 +814,7 @@ final class PhabricatorMetaMTAMail
    *                    recipients.
    * @return list<phid> Deaggregated list of mailable recipients.
    */
-  private function expandRecipients(array $phids) {
+  public function expandRecipients(array $phids) {
     if ($this->recipientExpansionMap === null) {
       $all_phids = $this->getAllActorPHIDs();
       $this->recipientExpansionMap = id(new PhabricatorMetaMTAMemberQuery())
@@ -1320,72 +1014,15 @@ final class PhabricatorMetaMTAMail
     return $actors;
   }
 
-  private function shouldRateLimitMail(array $all_recipients) {
-    try {
-      PhabricatorSystemActionEngine::willTakeAction(
-        $all_recipients,
-        new PhabricatorMetaMTAErrorMailAction(),
-        1);
-      return false;
-    } catch (PhabricatorSystemActionRateLimitException $ex) {
-      return true;
-    }
-  }
-
-  public function generateHeaders() {
-    $headers = array();
-
-    $headers[] = array('X-Phabricator-Sent-This-Message', 'Yes');
-    $headers[] = array('X-Mail-Transport-Agent', 'MetaMTA');
-
-    // Some clients respect this to suppress OOF and other auto-responses.
-    $headers[] = array('X-Auto-Response-Suppress', 'All');
-
-    $mailtags = $this->getParam('mailtags');
-    if ($mailtags) {
-      $tag_header = array();
-      foreach ($mailtags as $mailtag) {
-        $tag_header[] = '<'.$mailtag.'>';
-      }
-      $tag_header = implode(', ', $tag_header);
-      $headers[] = array('X-Phabricator-Mail-Tags', $tag_header);
-    }
-
-    $value = $this->getParam('headers', array());
-    foreach ($value as $pair) {
-      list($header_key, $header_value) = $pair;
-
-      // NOTE: If we have \n in a header, SES rejects the email.
-      $header_value = str_replace("\n", ' ', $header_value);
-      $headers[] = array($header_key, $header_value);
-    }
-
-    $is_bulk = $this->getParam('is-bulk');
-    if ($is_bulk) {
-      $headers[] = array('Precedence', 'bulk');
-    }
-
-    if ($this->getMustEncrypt()) {
-      $headers[] = array('X-Phabricator-Must-Encrypt', 'Yes');
-    }
-
-    $related_phid = $this->getRelatedPHID();
-    if ($related_phid) {
-      $headers[] = array('Thread-Topic', $related_phid);
-    }
-
-    $headers[] = array('X-Phabricator-Mail-ID', $this->getID());
-
-    $unique = Filesystem::readRandomCharacters(16);
-    $headers[] = array('X-Phabricator-Send-Attempt', $unique);
-
-    return $headers;
-  }
-
   public function getDeliveredHeaders() {
     return $this->getParam('headers.sent');
   }
 
+  public function setDeliveredHeaders(array $headers) {
+    $headers = $this->flattenHeaders($headers);
+    return $this->setParam('headers.sent', $headers);
+  }
+
   public function getUnfilteredHeaders() {
     $unfiltered = $this->getParam('headers.unfiltered');
 
@@ -1399,6 +1036,25 @@ final class PhabricatorMetaMTAMail
     return $unfiltered;
   }
 
+  public function setUnfilteredHeaders(array $headers) {
+    $headers = $this->flattenHeaders($headers);
+    return $this->setParam('headers.unfiltered', $headers);
+  }
+
+  private function flattenHeaders(array $headers) {
+    assert_instances_of($headers, 'PhabricatorMailHeader');
+
+    $list = array();
+    foreach ($list as $header) {
+      $list[] = array(
+        $header->getName(),
+        $header->getValue(),
+      );
+    }
+
+    return $list;
+  }
+
   public function getDeliveredActors() {
     return $this->getParam('actors.sent');
   }
@@ -1415,81 +1071,14 @@ final class PhabricatorMetaMTAMail
     return $this->getParam('body.sent');
   }
 
-  private function filterHeaders(array $headers, $must_encrypt) {
+  public function setDeliveredBody($body) {
-    if (!$must_encrypt) {
+    return $this->setParam('body.sent', $body);
-      return $headers;
-    }
-
-    $whitelist = array(
-      'In-Reply-To',
-      'Message-ID',
-      'Precedence',
-      'References',
-      'Thread-Index',
-      'Thread-Topic',
-
-      'X-Mail-Transport-Agent',
-      'X-Auto-Response-Suppress',
-
-      'X-Phabricator-Sent-This-Message',
-      'X-Phabricator-Must-Encrypt',
-      'X-Phabricator-Mail-ID',
-      'X-Phabricator-Send-Attempt',
-    );
-
-    // NOTE: The major header we want to drop is "X-Phabricator-Mail-Tags".
-    // This header contains a significant amount of meaningful information
-    // about the object.
-
-    $whitelist_map = array();
-    foreach ($whitelist as $term) {
-      $whitelist_map[phutil_utf8_strtolower($term)] = true;
-    }
-
-    foreach ($headers as $key => $header) {
-      list($name, $value) = $header;
-      $name = phutil_utf8_strtolower($name);
-
-      if (!isset($whitelist_map[$name])) {
-        unset($headers[$key]);
-      }
-    }
-
-    return $headers;
   }
 
   public function getURI() {
     return '/mail/detail/'.$this->getID().'/';
   }
 
-  private function newMailDomain() {
-    $domain = PhabricatorEnv::getEnvConfig('metamta.reply-handler-domain');
-    if (strlen($domain)) {
-      return $domain;
-    }
-
-    $install_uri = PhabricatorEnv::getURI('/');
-    $install_uri = new PhutilURI($install_uri);
-
-    return $install_uri->getDomain();
-  }
-
-  public function newDefaultEmailAddress() {
-    $raw_address = PhabricatorEnv::getEnvConfig('metamta.default-address');
-    if (strlen($raw_address)) {
-      return new PhutilEmailAddress($raw_address);
-    }
-
-    $domain = $this->newMailDomain();
-    $address = "noreply@{$domain}";
-
-    return new PhutilEmailAddress($address);
-  }
-
-  public function newVoidEmailAddress() {
-    return $this->newDefaultEmailAddress();
-  }
-
 
 /* -(  Routing  )------------------------------------------------------------ */
 
@@ -1578,27 +1167,6 @@ final class PhabricatorMetaMTAMail
     return PhabricatorUserPreferences::loadGlobalPreferences($viewer);
   }
 
-  private function shouldAddRePrefix(PhabricatorUserPreferences $preferences) {
-    $value = $preferences->getSettingValue(
-      PhabricatorEmailRePrefixSetting::SETTINGKEY);
-
-    return ($value == PhabricatorEmailRePrefixSetting::VALUE_RE_PREFIX);
-  }
-
-  private function shouldVarySubject(PhabricatorUserPreferences $preferences) {
-    $value = $preferences->getSettingValue(
-      PhabricatorEmailVarySubjectsSetting::SETTINGKEY);
-
-    return ($value == PhabricatorEmailVarySubjectsSetting::VALUE_VARY_SUBJECTS);
-  }
-
-  private function shouldSendHTML(PhabricatorUserPreferences $preferences) {
-    $value = $preferences->getSettingValue(
-      PhabricatorEmailFormatSetting::SETTINGKEY);
-
-    return ($value == PhabricatorEmailFormatSetting::VALUE_HTML_EMAIL);
-  }
-
   public function shouldRenderMailStampsInBody($viewer) {
     $preferences = $this->loadPreferences($viewer->getPHID());
     $value = $preferences->getSettingValue(