diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index a564ba0f3b..d1c833760c 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1185,6 +1185,7 @@ phutil_register_library_map(array(
     'PhabricatorObjectItemView' => 'view/layout/PhabricatorObjectItemView.php',
     'PhabricatorObjectListView' => 'view/control/PhabricatorObjectListView.php',
     'PhabricatorObjectMailReceiver' => 'applications/metamta/receiver/PhabricatorObjectMailReceiver.php',
+    'PhabricatorObjectMailReceiverTestCase' => 'applications/metamta/receiver/__tests__/PhabricatorObjectMailReceiverTestCase.php',
     'PhabricatorObjectSelectorDialog' => 'view/control/PhabricatorObjectSelectorDialog.php',
     'PhabricatorOffsetPagedQuery' => 'infrastructure/query/PhabricatorOffsetPagedQuery.php',
     'PhabricatorOwnerPathQuery' => 'applications/owners/query/PhabricatorOwnerPathQuery.php',
@@ -2920,6 +2921,7 @@ phutil_register_library_map(array(
     'PhabricatorObjectItemView' => 'AphrontTagView',
     'PhabricatorObjectListView' => 'AphrontView',
     'PhabricatorObjectMailReceiver' => 'PhabricatorMailReceiver',
+    'PhabricatorObjectMailReceiverTestCase' => 'PhabricatorTestCase',
     'PhabricatorOffsetPagedQuery' => 'PhabricatorQuery',
     'PhabricatorOwnersConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorOwnersController' => 'PhabricatorController',
diff --git a/src/applications/maniphest/lipsum/PhabricatorManiphestTaskTestDataGenerator.php b/src/applications/maniphest/lipsum/PhabricatorManiphestTaskTestDataGenerator.php
index 3245e19a76..494213eb59 100644
--- a/src/applications/maniphest/lipsum/PhabricatorManiphestTaskTestDataGenerator.php
+++ b/src/applications/maniphest/lipsum/PhabricatorManiphestTaskTestDataGenerator.php
@@ -72,7 +72,10 @@ final class PhabricatorManiphestTaskTestDataGenerator
   public function getProjectPHIDs() {
     $projects = array();
     for ($i = 0; $i < rand(1, 4);$i++) {
-      $projects[] = $this->loadOneRandom("PhabricatorProject")->getPHID();
+      $project = $this->loadOneRandom("PhabricatorProject");
+      if ($project) {
+        $projects[] = $project->getPHID();
+      }
     }
     return $projects;
   }
diff --git a/src/applications/metamta/constants/MetaMTAReceivedMailStatus.php b/src/applications/metamta/constants/MetaMTAReceivedMailStatus.php
index 7f1e477ad1..062fcbdfbe 100644
--- a/src/applications/metamta/constants/MetaMTAReceivedMailStatus.php
+++ b/src/applications/metamta/constants/MetaMTAReceivedMailStatus.php
@@ -8,5 +8,11 @@ final class MetaMTAReceivedMailStatus
   const STATUS_NO_RECEIVERS         = 'err:no-receivers';
   const STATUS_ABUNDANT_RECEIVERS   = 'err:multiple-receivers';
   const STATUS_UNKNOWN_SENDER       = 'err:unknown-sender';
+  const STATUS_DISABLED_SENDER      = 'err:disabled-sender';
+  const STATUS_NO_PUBLIC_MAIL       = 'err:no-public-mail';
+  const STATUS_USER_MISMATCH        = 'err:bad-user';
+  const STATUS_POLICY_PROBLEM       = 'err:policy';
+  const STATUS_NO_SUCH_OBJECT       = 'err:not-found';
+  const STATUS_HASH_MISMATCH        = 'err:bad-hash';
 
 }
diff --git a/src/applications/metamta/receiver/PhabricatorMailReceiver.php b/src/applications/metamta/receiver/PhabricatorMailReceiver.php
index 575aca6ff9..b44e67ac8b 100644
--- a/src/applications/metamta/receiver/PhabricatorMailReceiver.php
+++ b/src/applications/metamta/receiver/PhabricatorMailReceiver.php
@@ -6,6 +6,22 @@ abstract class PhabricatorMailReceiver {
   abstract public function isEnabled();
   abstract public function canAcceptMail(PhabricatorMetaMTAReceivedMail $mail);
 
+  public function validateSender(
+    PhabricatorMetaMTAReceivedMail $mail,
+    PhabricatorUser $sender) {
+
+    if ($sender->getIsDisabled()) {
+      throw new PhabricatorMetaMTAReceivedMailProcessingException(
+        MetaMTAReceivedMailStatus::STATUS_DISABLED_SENDER,
+        pht(
+          "Sender '%s' has a disabled user account.",
+          $sender->getUsername()));
+    }
+
+
+    return;
+  }
+
   /**
    * Identifies the sender's user account for a piece of received mail. Note
    * that this method does not validate that the sender is who they say they
diff --git a/src/applications/metamta/receiver/PhabricatorObjectMailReceiver.php b/src/applications/metamta/receiver/PhabricatorObjectMailReceiver.php
index 2fb0632be5..f429106f7d 100644
--- a/src/applications/metamta/receiver/PhabricatorObjectMailReceiver.php
+++ b/src/applications/metamta/receiver/PhabricatorObjectMailReceiver.php
@@ -2,15 +2,101 @@
 
 abstract class PhabricatorObjectMailReceiver extends PhabricatorMailReceiver {
 
+  /**
+   * Return a regular expression fragment which matches the name of an
+   * object which can receive mail. For example, Differential uses:
+   *
+   *  D[1-9]\d*
+   *
+   * ...to match `D123`, etc., identifying Differential Revisions.
+   *
+   * @return string Regular expression fragment.
+   */
   abstract protected function getObjectPattern();
 
-  final public function canAcceptMail(PhabricatorMetaMTAReceivedMail $mail) {
-    $regexp = $this->getAddressRegexp();
+
+  /**
+   * Load the object receiving mail, based on an identifying pattern. Normally
+   * this pattern is some sort of object ID.
+   *
+   * @param   string          A string matched by @{method:getObjectPattern}
+   *                          fragment.
+   * @param   PhabricatorUser The viewing user.
+   * @return  void
+   */
+  abstract protected function loadObject($pattern, PhabricatorUser $viewer);
+
+
+  public function validateSender(
+    PhabricatorMetaMTAReceivedMail $mail,
+    PhabricatorUser $sender) {
+    parent::validateSender($mail, $sender);
 
     foreach ($mail->getToAddresses() as $address) {
-      $address = self::stripMailboxPrefix($address);
-      $local = id(new PhutilEmailAddress($address))->getLocalPart();
-      if (preg_match($regexp, $local)) {
+      $parts = $this->matchObjectAddress($address);
+      if ($parts) {
+        break;
+      }
+    }
+
+    try {
+      $object = $this->loadObject($parts['pattern'], $sender);
+    } catch (PhabricatorPolicyException $policy_exception) {
+      throw new PhabricatorMetaMTAReceivedMailProcessingException(
+        MetaMTAReceivedMailStatus::STATUS_POLICY_PROBLEM,
+        pht(
+          "This mail is addressed to an object you are not permitted ".
+          "to see: %s",
+          $policy_exception->getMessage()));
+    }
+
+    if (!$object) {
+      throw new PhabricatorMetaMTAReceivedMailProcessingException(
+        MetaMTAReceivedMailStatus::STATUS_NO_SUCH_OBJECT,
+        pht(
+          "This mail is addressed to an object ('%s'), but that object ".
+          "does not exist.",
+          $parts['pattern']));
+    }
+
+    $sender_identifier = $parts['sender'];
+
+    if ($sender_identifier === 'public') {
+      if (!PhabricatorEnv::getEnvConfig('metamta.public-replies')) {
+        throw new PhabricatorMetaMTAReceivedMailProcessingException(
+          MetaMTAReceivedMailStatus::STATUS_NO_PUBLIC_MAIL,
+          pht(
+            "This mail is addressed to an object's public address, but ".
+            "public replies are not enabled (`metamta.public-replies`)."));
+      }
+      $check_phid = $object->getPHID();
+    } else {
+      if ($sender_identifier != $sender->getID()) {
+        throw new PhabricatorMetaMTAReceivedMailProcessingException(
+          MetaMTAReceivedMailStatus::STATUS_USER_MISMATCH,
+          pht(
+            "This mail is addressed to an object's private address, but ".
+            "the sending user and the private address owner are not the ".
+            "same user."));
+      }
+      $check_phid = $sender->getPHID();
+    }
+
+    $expect_hash = self::computeMailHash($object->getMailKey(), $check_phid);
+
+    if ($expect_hash != $parts['hash']) {
+      throw new PhabricatorMetaMTAReceivedMailProcessingException(
+        MetaMTAReceivedMailStatus::STATUS_HASH_MISMATCH,
+        pht(
+          "The hash in this object's address does not match the expected ".
+          "value."));
+    }
+  }
+
+
+  final public function canAcceptMail(PhabricatorMetaMTAReceivedMail $mail) {
+    foreach ($mail->getToAddresses() as $address) {
+      if ($this->matchObjectAddress($address)) {
         return true;
       }
     }
@@ -18,6 +104,20 @@ abstract class PhabricatorObjectMailReceiver extends PhabricatorMailReceiver {
     return false;
   }
 
+  private function matchObjectAddress($address) {
+    $regexp = $this->getAddressRegexp();
+
+    $address = self::stripMailboxPrefix($address);
+    $local = id(new PhutilEmailAddress($address))->getLocalPart();
+
+    $matches = null;
+    if (!preg_match($regexp, $local, $matches)) {
+      return false;
+    }
+
+    return $matches;
+  }
+
   private function getAddressRegexp() {
     $pattern = $this->getObjectPattern();
 
diff --git a/src/applications/metamta/receiver/__tests__/PhabricatorObjectMailReceiverTestCase.php b/src/applications/metamta/receiver/__tests__/PhabricatorObjectMailReceiverTestCase.php
new file mode 100644
index 0000000000..31ad44f974
--- /dev/null
+++ b/src/applications/metamta/receiver/__tests__/PhabricatorObjectMailReceiverTestCase.php
@@ -0,0 +1,128 @@
+<?php
+
+final class PhabricatorObjectMailReceiverTestCase
+  extends PhabricatorTestCase {
+
+  protected function getPhabricatorTestCaseConfiguration() {
+    return array(
+      self::PHABRICATOR_TESTCONFIG_BUILD_STORAGE_FIXTURES => true,
+    );
+  }
+
+  public function testDropUnconfiguredPublicMail() {
+    list($task, $user, $mail) = $this->buildMail('public');
+
+    $env = PhabricatorEnv::beginScopedEnv();
+    $env->overrideEnvConfig('metamta.public-replies', false);
+
+    $mail->save();
+    $mail->processReceivedMail();
+
+    $this->assertEqual(
+      MetaMTAReceivedMailStatus::STATUS_NO_PUBLIC_MAIL,
+      $mail->getStatus());
+  }
+
+/*
+
+  TODO: Tasks don't support policies yet. Implement this once they do.
+
+  public function testDropPolicyViolationMail() {
+    list($task, $user, $mail) = $this->buildMail('public');
+
+    // TODO: Set task policy to "no one" here.
+
+    $mail->save();
+    $mail->processReceivedMail();
+
+    $this->assertEqual(
+      MetaMTAReceivedMailStatus::STATUS_POLICY_PROBLEM,
+      $mail->getStatus());
+  }
+
+*/
+
+  public function testDropInvalidObjectMail() {
+    list($task, $user, $mail) = $this->buildMail('404');
+
+    $mail->save();
+    $mail->processReceivedMail();
+
+    $this->assertEqual(
+      MetaMTAReceivedMailStatus::STATUS_NO_SUCH_OBJECT,
+      $mail->getStatus());
+  }
+
+  public function testDropUserMismatchMail() {
+    list($task, $user, $mail) = $this->buildMail('baduser');
+
+    $mail->save();
+    $mail->processReceivedMail();
+
+    $this->assertEqual(
+      MetaMTAReceivedMailStatus::STATUS_USER_MISMATCH,
+      $mail->getStatus());
+  }
+
+  public function testDropHashMismatchMail() {
+    list($task, $user, $mail) = $this->buildMail('badhash');
+
+    $mail->save();
+    $mail->processReceivedMail();
+
+    $this->assertEqual(
+      MetaMTAReceivedMailStatus::STATUS_HASH_MISMATCH,
+      $mail->getStatus());
+  }
+
+  private function buildMail($style) {
+
+    // TODO: Clean up test data generators so that we don't need to guarantee
+    // the existence of a user.
+    $this->generateNewTestUser();
+
+    $task = id(new PhabricatorManiphestTaskTestDataGenerator())->generate();
+    $user = $this->generateNewTestUser();
+
+    $is_public = ($style === 'public');
+    $is_bad_hash = ($style == 'badhash');
+    $is_bad_user = ($style == 'baduser');
+    $is_404_object = ($style == '404');
+
+    if ($is_public) {
+      $user_identifier = 'public';
+    } else if ($is_bad_user) {
+      $user_identifier = $user->getID() + 1;
+    } else {
+      $user_identifier = $user->getID();
+    }
+
+    if ($is_bad_hash) {
+      $hash = PhabricatorObjectMailReceiver::computeMailHash('x', 'y');
+    } else {
+      $hash = PhabricatorObjectMailReceiver::computeMailHash(
+        $task->getMailKey(),
+        $is_public ? $task->getPHID() : $user->getPHID());
+    }
+
+    if ($is_404_object) {
+      $task_identifier = 'T'.($task->getID() + 1);
+    } else {
+      $task_identifier = 'T'.$task->getID();
+    }
+
+    $to = $task_identifier.'+'.$user_identifier.'+'.$hash.'@example.com';
+
+    $mail = new PhabricatorMetaMTAReceivedMail();
+    $mail->setHeaders(
+      array(
+        'Message-ID' => 'test@example.com',
+        'From'       => $user->loadPrimaryEmail()->getAddress(),
+        'To'         => $to,
+      ));
+
+    return array($task, $user, $mail);
+  }
+
+
+}
diff --git a/src/applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php b/src/applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php
index ff1ec8f631..e4e360fc30 100644
--- a/src/applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php
+++ b/src/applications/metamta/storage/PhabricatorMetaMTAReceivedMail.php
@@ -176,6 +176,7 @@ final class PhabricatorMetaMTAReceivedMail extends PhabricatorMetaMTADAO {
 
       $receiver = $this->loadReceiver();
       $sender = $receiver->loadSender($this);
+      $receiver->validateSender($this, $sender);
 
     } catch (PhabricatorMetaMTAReceivedMailProcessingException $ex) {
       $this
@@ -197,62 +198,11 @@ final class PhabricatorMetaMTAReceivedMail extends PhabricatorMetaMTADAO {
 
     $from = idx($this->headers, 'from');
 
-    // TODO -- make this a switch statement / better if / when we add more
-    // public create email addresses!
-    $create_task = PhabricatorEnv::getEnvConfig(
-      'metamta.maniphest.public-create-email');
-
-    if ($create_task && $to == $create_task) {
+    // TODO: Move this into `ManiphestCreateMailReceiver`.
+    if ($receiver instanceof ManiphestCreateMailReceiver) {
       $receiver = new ManiphestTask();
 
-      $user = $this->lookupSender();
-      if ($user) {
-        $this->setAuthorPHID($user->getPHID());
-      } else {
-        $allow_email_users = PhabricatorEnv::getEnvConfig(
-          'phabricator.allow-email-users');
-
-        if ($allow_email_users) {
-          $email = new PhutilEmailAddress($from);
-
-          $xuser = id(new PhabricatorExternalAccount())->loadOneWhere(
-            'accountType = %s AND accountDomain IS NULL and accountID = %s',
-            'email',
-            $email->getAddress());
-
-          if (!$xuser) {
-            $xuser = new PhabricatorExternalAccount();
-            $xuser->setAccountID($email->getAddress());
-            $xuser->setAccountType('email');
-            $xuser->setDisplayName($email->getDisplayName());
-            $xuser->save();
-          }
-
-          $user = $xuser->getPhabricatorUser();
-        } else {
-          $default_author = PhabricatorEnv::getEnvConfig(
-            'metamta.maniphest.default-public-author');
-
-          if ($default_author) {
-            $user = id(new PhabricatorUser())->loadOneWhere(
-              'username = %s',
-              $default_author);
-
-            if (!$user) {
-              throw new Exception(
-                "Phabricator is misconfigured, the configuration key ".
-                "'metamta.maniphest.default-public-author' is set to user ".
-                "'{$default_author}' but that user does not exist.");
-            }
-
-          } else {
-            // TODO: We should probably bounce these since from the user's
-            // perspective their email vanishes into a black hole.
-            return $this->setMessage("Invalid public user '{$from}'.")->save();
-          }
-        }
-
-      }
+      $user = $sender;
 
       $receiver->setAuthorPHID($user->getPHID());
       $receiver->setOriginalEmailSource($from);
@@ -275,11 +225,7 @@ final class PhabricatorMetaMTAReceivedMail extends PhabricatorMetaMTADAO {
 
     // means we're creating a conpherence...!
     if ($user_phids) {
-      // we must have a valid user who created this conpherence
-      $user = $this->lookupSender();
-      if (!$user) {
-        return $this->setMessage("Invalid public user '{$from}'.")->save();
-      }
+      $user = $sender;
 
       $conpherence = id(new ConpherenceReplyHandler())
         ->setMailReceiver(new ConpherenceThread())
@@ -293,31 +239,7 @@ final class PhabricatorMetaMTAReceivedMail extends PhabricatorMetaMTADAO {
       return $this->save();
     }
 
-    if ($user_id == 'public') {
-      if (!PhabricatorEnv::getEnvConfig('metamta.public-replies')) {
-        return $this->setMessage("Public replies not enabled.")->save();
-      }
-
-      $user = $this->lookupSender();
-
-      if (!$user) {
-        return $this->setMessage("Invalid public user '{$from}'.")->save();
-      }
-
-      $use_user_hash = false;
-    } else {
-      $user = id(new PhabricatorUser())->load($user_id);
-      if (!$user) {
-        return $this->setMessage("Invalid private user '{$user_id}'.")->save();
-      }
-
-      $use_user_hash = true;
-    }
-
-    if ($user->getIsDisabled()) {
-      return $this->setMessage("User '{$user_id}' is disabled")->save();
-    }
-
+    $user = $sender;
     $this->setAuthorPHID($user->getPHID());
 
     $receiver = self::loadReceiverObject($receiver_name);
@@ -327,24 +249,6 @@ final class PhabricatorMetaMTAReceivedMail extends PhabricatorMetaMTADAO {
 
     $this->setRelatedPHID($receiver->getPHID());
 
-    if ($use_user_hash) {
-      // This is a private reply-to address, check that the user hash is
-      // correct.
-      $check_phid = $user->getPHID();
-    } else {
-      // This is a public reply-to address, check that the object hash is
-      // correct.
-      $check_phid = $receiver->getPHID();
-    }
-
-    $expect_hash = PhabricatorObjectMailReceiver::computeMailHash(
-      $receiver->getMailKey(),
-      $check_phid);
-
-    if ($expect_hash != $hash) {
-      return $this->setMessage("Invalid mail hash!")->save();
-    }
-
     if ($receiver instanceof ManiphestTask) {
       $editor = new ManiphestTransactionEditor();
       $editor->setActor($user);
@@ -431,39 +335,6 @@ final class PhabricatorMetaMTAReceivedMail extends PhabricatorMetaMTADAO {
     return array_filter($raw_addresses);
   }
 
-  private function lookupSender() {
-    $from = idx($this->headers, 'from');
-    $from = $this->getRawEmailAddress($from);
-
-    $user = PhabricatorUser::loadOneWithEmailAddress($from);
-
-    // If Phabricator is configured to allow "Reply-To" authentication, try
-    // the "Reply-To" address if we failed to match the "From" address.
-    $config_key = 'metamta.insecure-auth-with-reply-to';
-    $allow_reply_to = PhabricatorEnv::getEnvConfig($config_key);
-
-    if (!$user && $allow_reply_to) {
-      $reply_to = idx($this->headers, 'reply-to');
-      $reply_to = $this->getRawEmailAddress($reply_to);
-      if ($reply_to) {
-        $user = PhabricatorUser::loadOneWithEmailAddress($reply_to);
-      }
-    }
-
-    $allow_email_users = PhabricatorEnv::getEnvConfig(
-          'phabricator.allow-email-users');
-
-    if (!$user && $allow_email_users) {
-      $xusr = id(new PhabricatorExternalAccount())->loadOneWhere(
-            'accountType = %s AND accountDomain IS NULL and accountID = %s',
-            'email', $from);
-
-      $user = $xusr->getPhabricatorUser();
-    }
-
-    return $user;
-  }
-
   /**
    * If Phabricator sent the mail, always drop it immediately. This prevents
    * loops where, e.g., the public bug address is also a user email address
diff --git a/src/applications/metamta/storage/__tests__/PhabricatorMetaMTAReceivedMailTestCase.php b/src/applications/metamta/storage/__tests__/PhabricatorMetaMTAReceivedMailTestCase.php
index 1e1be9c566..8f3e72a342 100644
--- a/src/applications/metamta/storage/__tests__/PhabricatorMetaMTAReceivedMailTestCase.php
+++ b/src/applications/metamta/storage/__tests__/PhabricatorMetaMTAReceivedMailTestCase.php
@@ -87,4 +87,31 @@ final class PhabricatorMetaMTAReceivedMailTestCase extends PhabricatorTestCase {
       $mail->getStatus());
   }
 
+
+  public function testDropDisabledSenderMail() {
+    $env = PhabricatorEnv::beginScopedEnv();
+    $env->overrideEnvConfig(
+      'metamta.maniphest.public-create-email',
+      'bugs@example.com');
+
+    $user = $this->generateNewTestUser()
+      ->setIsDisabled(true)
+      ->save();
+
+    $mail = new PhabricatorMetaMTAReceivedMail();
+    $mail->setHeaders(
+      array(
+        'Message-ID'  => 'test@example.com',
+        'From'        => $user->loadPrimaryEmail()->getAddress(),
+        'To'          => 'bugs@example.com',
+      ));
+    $mail->save();
+
+    $mail->processReceivedMail();
+
+    $this->assertEqual(
+      MetaMTAReceivedMailStatus::STATUS_DISABLED_SENDER,
+      $mail->getStatus());
+  }
+
 }