diff --git a/src/applications/audit/editor/PhabricatorAuditCommentEditor.php b/src/applications/audit/editor/PhabricatorAuditCommentEditor.php
--- a/src/applications/audit/editor/PhabricatorAuditCommentEditor.php
+++ b/src/applications/audit/editor/PhabricatorAuditCommentEditor.php
@@ -420,7 +420,7 @@
     $threading = self::getMailThreading($repository, $commit);
     list($thread_id, $thread_topic) = $threading;
 
-    $body = $this->renderMailBody(
+    $body = $this->buildMailBody(
       $comment,
       "{$name}: {$summary}",
       $handle,
@@ -480,7 +480,8 @@
       ->setRelatedPHID($commit->getPHID())
       ->setExcludeMailRecipientPHIDs($this->getExcludeMailRecipientPHIDs())
       ->setIsBulk(true)
-      ->setBody($body);
+      ->setBody($body->render())
+      ->setHTMLBody($body->renderHTML());
 
     $mails = $reply_handler->multiplexMail(
       $template,
@@ -509,7 +510,7 @@
     return $reply_handler;
   }
 
-  private function renderMailBody(
+  private function buildMailBody(
     PhabricatorAuditComment $comment,
     $cname,
     PhabricatorObjectHandle $handle,
@@ -562,7 +563,7 @@
       PhabricatorEnv::getProductionURI($handle->getURI()));
     $body->addReplySection($reply_handler->getReplyHandlerInstructions());
 
-    return $body->render();
+    return $body;
   }
 
 }
diff --git a/src/applications/config/option/PhabricatorMetaMTAConfigOptions.php b/src/applications/config/option/PhabricatorMetaMTAConfigOptions.php
--- a/src/applications/config/option/PhabricatorMetaMTAConfigOptions.php
+++ b/src/applications/config/option/PhabricatorMetaMTAConfigOptions.php
@@ -331,7 +331,21 @@
             'in bytes.'))
         ->setSummary(pht('Global cap for size of generated emails (bytes).'))
         ->addExample(524288, pht('Truncate at 512KB'))
-        ->addExample(1048576, pht('Truncate at 1MB'))
+        ->addExample(1048576, pht('Truncate at 1MB')),
+      $this->newOption('metamta.html-emails', 'bool', false)
+        ->setBoolOptions(
+          array(
+            pht('Enable HTML emails'),
+            pht('Plaintext emails only'),
+          ))
+        ->setSummary(
+          pht(
+            'Phabricator can send prettier emails when HTML is enabled '.
+            'reply addresses.'))
+        ->setDescription(
+          pht('HTML emails offer prettier emails (colorized diffs, links etc)'.
+              ', however it may reduce the reliability of reply-by-email')),
+
     );
   }
 
diff --git a/src/applications/differential/editor/DifferentialTransactionEditor.php b/src/applications/differential/editor/DifferentialTransactionEditor.php
--- a/src/applications/differential/editor/DifferentialTransactionEditor.php
+++ b/src/applications/differential/editor/DifferentialTransactionEditor.php
@@ -1164,13 +1164,16 @@
       $config_attach = PhabricatorEnv::getEnvConfig($config_key_attach);
 
       if ($config_inline || $config_attach) {
-        $patch = $this->renderPatchForMail($diff);
+        list($patch, $html_patch) = $this->renderPatchForMail($diff);
         $lines = count(phutil_split_lines($patch));
 
         if ($config_inline && ($lines <= $config_inline)) {
-          $body->addTextSection(
+          $body->addPlaintextSection(
             pht('CHANGE DETAILS'),
             $patch);
+          $body->addHTMLSection(
+            pht('CHANGE DETAILS'),
+            $html_patch);
         }
 
         if ($config_attach) {
@@ -1697,11 +1700,38 @@
   private function renderPatchForMail(DifferentialDiff $diff) {
     $format = PhabricatorEnv::getEnvConfig('metamta.differential.patch-format');
 
-    return id(new DifferentialRawDiffRenderer())
+    $patch = id(new DifferentialRawDiffRenderer())
       ->setViewer($this->getActor())
       ->setFormat($format)
       ->setChangesets($diff->getChangesets())
       ->buildPatch();
+
+    // some basic formatting (switch to a PhutilSyntaxHighlighterEngine?)
+    $patch_html_lines = array();
+    foreach (phutil_split_lines($patch) as $line) {
+      $len = strlen($line);
+      $color = null;
+      if ($len >= 1 && $line[0] == '+') {
+        $color = 'green';
+      } else if ($len >= 1 && $line[0] == '-') {
+        $color = 'red';
+      } else if ($len >= 2 && substr($line, 0, 2) == '@@') {
+        $color = 'purple';
+      }
+
+      $attrib = array();
+
+      if ($color) {
+        $attrib['style'] = "color:{$color};";
+      }
+
+      $patch_html_lines[] = phutil_tag('span', $attrib, $line);
+    }
+
+    $html_patch = "<pre style='font-family: monospace;'>".
+      implode('', $patch_html_lines).'</pre>';
+
+    return array($patch, $html_patch);
   }
 
 }
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
@@ -8,9 +8,9 @@
   abstract public function addCCs(array $emails);
   abstract public function addAttachment($data, $filename, $mimetype);
   abstract public function addHeader($header_name, $header_value);
-  abstract public function setBody($body);
+  abstract public function setBody($plaintext_body);
+  abstract public function setHTMLBody($html_body);
   abstract public function setSubject($subject);
-  abstract public function setIsHTML($is_html);
 
   /**
    * Some mailers, notably Amazon SES, do not support us setting a specific
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
@@ -57,13 +57,13 @@
     return $this;
   }
 
-  public function setSubject($subject) {
-    $this->params['subject'] = $subject;
+  public function setHTMLBody($html_body) {
+    $this->params['html-body'] = $html_body;
     return $this;
   }
 
-  public function setIsHTML($is_html) {
-    $this->params['is-html'] = $is_html;
+  public function setSubject($subject) {
+    $this->params['subject'] = $subject;
     return $this;
   }
 
@@ -78,11 +78,10 @@
 
     $params['to'] = implode(', ', idx($this->params, 'tos', array()));
     $params['subject'] = idx($this->params, 'subject');
+    $params['text'] = idx($this->params, 'body');
 
-    if (idx($this->params, 'is-html')) {
-      $params['html'] = idx($this->params, 'body');
-    } else {
-      $params['text'] = idx($this->params, 'body');
+    if (idx($this->params, 'html-body')) {
+      $params['html'] = idx($this->params, 'html-body');
     }
 
     $from = idx($this->params, 'from');
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
@@ -91,17 +91,19 @@
   }
 
   public function setBody($body) {
+    $this->mailer->IsHTML(false);
     $this->mailer->Body = $body;
     return $this;
   }
 
-  public function setSubject($subject) {
-    $this->mailer->Subject = $subject;
+  public function setHTMLBody($html_body) {
+    $this->mailer->IsHTML(true);
+    $this->mailer->Body = $html_body;
     return $this;
   }
 
-  public function setIsHTML($is_html) {
-    $this->mailer->IsHTML($is_html);
+  public function setSubject($subject) {
+    $this->mailer->Subject = $subject;
     return $this;
   }
 
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
@@ -70,16 +70,23 @@
 
   public function setBody($body) {
     $this->mailer->Body = $body;
+    $this->mailer->IsHTML(false);
     return $this;
   }
 
-  public function setSubject($subject) {
-    $this->mailer->Subject = $subject;
+
+  /** Note: phpmailer-lite does NOT support sending messages with mixed version
+   * (plaintext and html). So for now lets just use HTML if it's available.
+   * @param $html
+   */
+  public function setHTMLBody($html_body) {
+    $this->mailer->Body = $html_body;
+    $this->mailer->IsHTML(true);
     return $this;
   }
 
-  public function setIsHTML($is_html) {
-    $this->mailer->IsHTML($is_html);
+  public function setSubject($subject) {
+    $this->mailer->Subject = $subject;
     return $this;
   }
 
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
@@ -56,13 +56,14 @@
     return $this;
   }
 
-  public function setSubject($subject) {
-    $this->params['subject'] = $subject;
+  public function setHTMLBody($body) {
+    $this->params['html-body'] = $body;
     return $this;
   }
 
-  public function setIsHTML($is_html) {
-    $this->params['is-html'] = $is_html;
+
+  public function setSubject($subject) {
+    $this->params['subject'] = $subject;
     return $this;
   }
 
@@ -89,10 +90,10 @@
     }
 
     $params['subject'] = idx($this->params, 'subject');
-    if (idx($this->params, 'is-html')) {
-      $params['html'] = idx($this->params, 'body');
-    } else {
-      $params['text'] = idx($this->params, 'body');
+    $params['text'] = idx($this->params, 'body');
+
+    if (idx($this->params, 'html-body')) {
+      $params['html'] = idx($this->params, 'html-body');
     }
 
     $params['from'] = idx($this->params, 'from');
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
@@ -64,13 +64,13 @@
     return $this;
   }
 
-  public function setSubject($subject) {
-    $this->guts['subject'] = $subject;
+  public function setHTMLBody($html_body) {
+    $this->guts['html-body'] = $html_body;
     return $this;
   }
 
-  public function setIsHTML($is_html) {
-    $this->guts['is-html'] = $is_html;
+  public function setSubject($subject) {
+    $this->guts['subject'] = $subject;
     return $this;
   }
 
diff --git a/src/applications/metamta/management/PhabricatorMailManagementSendTestWorkflow.php b/src/applications/metamta/management/PhabricatorMailManagementSendTestWorkflow.php
--- a/src/applications/metamta/management/PhabricatorMailManagementSendTestWorkflow.php
+++ b/src/applications/metamta/management/PhabricatorMailManagementSendTestWorkflow.php
@@ -105,7 +105,6 @@
     $subject = $args->getArg('subject');
     $tags = $args->getArg('tag');
     $attach = $args->getArg('attach');
-    $is_html = $args->getArg('html');
     $is_bulk = $args->getArg('bulk');
 
     $console->writeErr("%s\n", pht('Reading message body from stdin...'));
@@ -116,12 +115,17 @@
       ->addTos($tos)
       ->addCCs($ccs)
       ->setSubject($subject)
-      ->setBody($body)
       ->setOverrideNoSelfMailPreference(true)
-      ->setIsHTML($is_html)
       ->setIsBulk($is_bulk)
       ->setMailTags($tags);
 
+    if ($args->getArg('html')) {
+      $mail->setBody('plaintext email');
+      $mail->setHTMLBody($body);
+    } else {
+      $mail->setBody($body);
+    }
+
     if ($from) {
       $mail->setFrom($from->getPHID());
     }
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
@@ -213,13 +213,12 @@
     return $this;
   }
 
-  public function getBody() {
-    return $this->getParam('body');
+  public function setHTMLBody($html) {
+    $this->setParam('html-body', $html);
   }
 
-  public function setIsHTML($html) {
-    $this->setParam('is-html', $html);
-    return $this;
+  public function getBody() {
+    return $this->getParam('body');
   }
 
   public function setIsErrorEmail($is_error) {
@@ -425,15 +424,6 @@
                 $attachment->getMimeType());
             }
             break;
-          case 'body':
-            $max = PhabricatorEnv::getEnvConfig('metamta.email-body-limit');
-            if (strlen($value) > $max) {
-              $value = phutil_utf8_shorten($value, $max);
-              $value .= "\n";
-              $value .= pht('(This email was truncated at %d bytes.)', $max);
-            }
-            $mailer->setBody($value);
-            break;
           case 'subject':
             // Only try to use preferences if everything is multiplexed, so we
             // get consistent behavior.
@@ -499,11 +489,6 @@
 
             $mailer->setSubject(implode(' ', array_filter($subject)));
             break;
-          case 'is-html':
-            if ($value) {
-              $mailer->setIsHTML(true);
-            }
-            break;
           case 'is-bulk':
             if ($value) {
               if (PhabricatorEnv::getEnvConfig('metamta.precedence-bulk')) {
@@ -551,6 +536,20 @@
         }
       }
 
+      $body = $params['body'];
+      $max = PhabricatorEnv::getEnvConfig('metamta.email-body-limit');
+      if (strlen($body) > $max) {
+        $body = phutil_utf8_shorten($body, $max);
+        $body .= "\n";
+        $body .= pht('(This email was truncated at %d bytes.)', $max);
+      }
+      $mailer->setBody($body);
+
+      if (PhabricatorEnv::getEnvConfig('metamta.html-emails') &&
+          isset($params['html-body'])) {
+        $mailer->setHTMLBody($params['html-body']);
+      }
+
       if (!$add_to && !$add_cc) {
         $this->setStatus(self::STATUS_VOID);
         $this->setMessage(
diff --git a/src/applications/metamta/view/PhabricatorMetaMTAMailBody.php b/src/applications/metamta/view/PhabricatorMetaMTAMailBody.php
--- a/src/applications/metamta/view/PhabricatorMetaMTAMailBody.php
+++ b/src/applications/metamta/view/PhabricatorMetaMTAMailBody.php
@@ -10,6 +10,7 @@
 final class PhabricatorMetaMTAMailBody {
 
   private $sections = array();
+  private $htmlSections = array();
   private $attachments = array();
 
 
@@ -25,11 +26,28 @@
    */
   public function addRawSection($text) {
     if (strlen($text)) {
-      $this->sections[] = rtrim($text);
+      $text = rtrim($text);
+      $this->sections[] = $text;
+      $this->htmlSections[] = phutil_escape_html_newlines(
+        phutil_tag('div', array(), $text));
     }
     return $this;
   }
 
+  public function addRawPlaintextSection($text) {
+    if (strlen($text)) {
+      $text = rtrim($text);
+      $this->sections[] = $text;
+    }
+    return $this;
+  }
+
+  public function addRawHTMLSection($html) {
+    if (strlen($html)) {
+      $this->htmlSections[] = $html;
+    }
+    return $this;
+  }
 
   /**
    * Add a block of text with a section header. This is rendered like this:
@@ -43,10 +61,26 @@
    * @task compose
    */
   public function addTextSection($header, $text) {
+    $this->addPlaintextSection($header, $text);
+    $this->addHTMLSection($header,
+      phutil_escape_html_newlines(phutil_tag('div', array(), $text)));
+    return $this;
+  }
+
+  public function addPlaintextSection($header, $text) {
     $this->sections[] = $header."\n".$this->indent($text);
     return $this;
   }
 
+  public function addHTMLSection($header, $html_fragment) {
+    $this->htmlSections[] = phutil_tag('div',
+      array(
+        'style' => 'font-weight:800;'
+      ),
+      $header).$html_fragment;
+
+    return $this;
+  }
 
   /**
    * Add a Herald section with a rule management URI and a transcript URI.
@@ -115,6 +149,9 @@
     return implode("\n\n", $this->sections)."\n";
   }
 
+  public function renderHTML() {
+    return implode('<br><br>', $this->htmlSections).'<br>';
+  }
 
   /**
    * Retrieve attachments.
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -1810,7 +1810,8 @@
       ->setExcludeMailRecipientPHIDs($this->getExcludeMailRecipientPHIDs())
       ->setMailTags($mail_tags)
       ->setIsBulk(true)
-      ->setBody($body->render());
+      ->setBody($body->render())
+      ->setHTMLBody($body->renderHTML());
 
     foreach ($body->getAttachments() as $attachment) {
       $template->addAttachment($attachment);
@@ -1998,6 +1999,7 @@
     array $xactions) {
 
     $headers = array();
+    $html_headers = array();
     $comments = array();
 
     foreach ($xactions as $xaction) {
@@ -2008,6 +2010,9 @@
       $header = $xaction->getTitleForMail();
       if ($header !== null) {
         $headers[] = $header;
+        $html_headers[] = phutil_tag('span', array(
+          'style' => 'color:'.$xaction->getColor()
+        ), $header);
       }
 
       $comment = $xaction->getBodyForMail();
@@ -2017,7 +2022,8 @@
     }
 
     $body = new PhabricatorMetaMTAMailBody();
-    $body->addRawSection(implode("\n", $headers));
+    $body->addRawPlaintextSection(implode("\n", $headers));
+    $body->addRawHTMLSection(implode('<br>', $html_headers));
 
     foreach ($comments as $comment) {
       $body->addRawSection($comment);