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
@@ -1629,6 +1629,7 @@
     'PhabricatorMail' => 'applications/metamta/PhabricatorMail.php',
     'PhabricatorMailImplementationAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationAdapter.php',
     'PhabricatorMailImplementationAmazonSESAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php',
+    'PhabricatorMailImplementationFileTestAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationFileTestAdapter.php',
     'PhabricatorMailImplementationMailgunAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php',
     'PhabricatorMailImplementationPHPMailerAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php',
     'PhabricatorMailImplementationPHPMailerLiteAdapter' => 'applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php',
@@ -4379,6 +4380,7 @@
     'PhabricatorMacroTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
     'PhabricatorMacroViewController' => 'PhabricatorMacroController',
     'PhabricatorMailImplementationAmazonSESAdapter' => 'PhabricatorMailImplementationPHPMailerLiteAdapter',
+    'PhabricatorMailImplementationFileTestAdapter' => 'PhabricatorMailImplementationAdapter',
     'PhabricatorMailImplementationMailgunAdapter' => 'PhabricatorMailImplementationAdapter',
     'PhabricatorMailImplementationPHPMailerAdapter' => 'PhabricatorMailImplementationAdapter',
     'PhabricatorMailImplementationPHPMailerLiteAdapter' => 'PhabricatorMailImplementationAdapter',
diff --git a/src/applications/harbormaster/engine/HarbormasterBuildEngine.php b/src/applications/harbormaster/engine/HarbormasterBuildEngine.php
--- a/src/applications/harbormaster/engine/HarbormasterBuildEngine.php
+++ b/src/applications/harbormaster/engine/HarbormasterBuildEngine.php
@@ -183,6 +183,9 @@
     if (count($failed)) {
       $build->setBuildStatus(HarbormasterBuild::STATUS_FAILED);
       $build->save();
+
+      $this->handleFailedBuild($build);
+
       return;
     }
 
@@ -191,6 +194,9 @@
     if (count($complete) == count($steps)) {
       $build->setBuildStatus(HarbormasterBuild::STATUS_PASSED);
       $build->save();
+
+      $this->handlePassedBuild($build);
+
       return;
     }
 
@@ -231,6 +237,9 @@
       // normally be possible, but we should communicate it more clearly.
       $build->setBuildStatus(HarbormasterBuild::STATUS_FAILED);
       $build->save();
+
+      $this->handleFailedBuild($build);
+
       return;
     }
 
@@ -245,4 +254,62 @@
     }
   }
 
+  private function handleFailedBuild(HarbormasterBuild $build) {
+    $subscribers = PhabricatorSubscribersQuery::loadSubscribersForPHID(
+      $build->getBuildPlanPHID());
+
+    $build_uri = new PhutilURI('/harbormaster/build/'.$build->getID().'/');
+    $prod_uri = PhabricatorEnv::getProductionURI('');
+
+    // TODO: Do we need to check to see if the subscriber can see
+    // the buildable this build applies to?
+
+    // TODO: Include more information
+
+    $body = pht('Link to build: %s', $prod_uri.$build_uri);
+
+    $subject = pht('Build ').$build->getID();
+
+    $mail = new PhabricatorMetaMTAMail();
+    $mail->setSubject($subject)
+      ->setSubjectPrefix('[Harbormaster]')
+      ->setVarySubjectPrefix('[Build Failed]')
+      ->addHeader('Thread-Topic', pht('Build Failed ').$build->getID())
+      ->addTos($subscribers)
+      ->setBody($body)
+      ->setRelatedPHID($build->getPHID())
+      ->setIsBulk(true);
+
+    $mail->saveAndSend();
+  }
+
+  private function handlePassedBuild(HarbormasterBuild $build) {
+    $subscribers = PhabricatorSubscribersQuery::loadSubscribersForPHID(
+      $build->getBuildPlanPHID());
+
+    $build_uri = new PhutilURI('/harbormaster/build/'.$build->getID().'/');
+    $prod_uri = PhabricatorEnv::getProductionURI('');
+
+    // TODO: Do we need to check to see if the subscriber can see
+    // the buildable this build applies to?
+
+    // TODO: Include more information
+
+    $body = pht('Link to build: %s', $prod_uri.$build_uri);
+
+    $subject = pht('Build ').$build->getID();
+
+    $mail = new PhabricatorMetaMTAMail();
+    $mail->setSubject($subject)
+      ->setSubjectPrefix('[Harbormaster]')
+      ->setVarySubjectPrefix('[Build Passed]')
+      ->addHeader('Thread-Topic', pht('Build Passed ').$build->getID())
+      ->addTos($subscribers)
+      ->setBody($body)
+      ->setRelatedPHID($build->getPHID())
+      ->setIsBulk(true);
+
+    $mail->saveAndSend();
+  }
+
 }
diff --git a/src/applications/metamta/adapter/PhabricatorMailImplementationFileTestAdapter.php b/src/applications/metamta/adapter/PhabricatorMailImplementationFileTestAdapter.php
new file mode 100644
--- /dev/null
+++ b/src/applications/metamta/adapter/PhabricatorMailImplementationFileTestAdapter.php
@@ -0,0 +1,95 @@
+<?php
+
+/**
+ * Mail adapter that writes emails to Phabricator Files (for local testing).
+ */
+final class PhabricatorMailImplementationFileTestAdapter
+  extends PhabricatorMailImplementationAdapter {
+
+  private $guts = array();
+  private $config;
+
+  public function __construct(array $config = array()) {
+    $this->config = $config;
+  }
+
+  public function setFrom($email, $name = '') {
+    $this->guts['from'] = $email;
+    $this->guts['from-name'] = $name;
+    return $this;
+  }
+
+  public function addReplyTo($email, $name = '') {
+    if (empty($this->guts['reply-to'])) {
+      $this->guts['reply-to'] = array();
+    }
+    $this->guts['reply-to'][] = array(
+      'email' => $email,
+      'name'  => $name,
+    );
+    return $this;
+  }
+
+  public function addTos(array $emails) {
+    foreach ($emails as $email) {
+      $this->guts['tos'][] = $email;
+    }
+    return $this;
+  }
+
+  public function addCCs(array $emails) {
+    foreach ($emails as $email) {
+      $this->guts['ccs'][] = $email;
+    }
+    return $this;
+  }
+
+  public function addAttachment($data, $filename, $mimetype) {
+    $this->guts['attachments'][] = array(
+      'data' => $data,
+      'filename' => $filename,
+      'mimetype' => $mimetype
+    );
+    return $this;
+  }
+
+  public function addHeader($header_name, $header_value) {
+    $this->guts['headers'][] = array($header_name, $header_value);
+    return $this;
+  }
+
+  public function setBody($body) {
+    $this->guts['body'] = $body;
+    return $this;
+  }
+
+  public function setSubject($subject) {
+    $this->guts['subject'] = $subject;
+    return $this;
+  }
+
+  public function setIsHTML($is_html) {
+    $this->guts['is-html'] = $is_html;
+    return $this;
+  }
+
+  public function supportsMessageIDHeader() {
+    return $this->config['supportsMessageIDHeader'];
+  }
+
+  public function send() {
+    $this->guts['did-send'] = true;
+
+    $file = PhabricatorFile::newFromFileData(
+      json_encode($this->guts, JSON_PRETTY_PRINT),
+      array(
+        'name' => time().'.mail.txt',
+        'ttl' => time() + (5 * 60)));
+
+    return true;
+  }
+
+  public function getGuts() {
+    return $this->guts;
+  }
+}