diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index 116886402e..f924623cb0 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -3025,6 +3025,7 @@ phutil_register_library_map(array(
     'PonderVoteSaveController' => 'applications/ponder/controller/PonderVoteSaveController.php',
     'PonderVotingUserHasAnswerEdgeType' => 'applications/ponder/edge/PonderVotingUserHasAnswerEdgeType.php',
     'PonderVotingUserHasQuestionEdgeType' => 'applications/ponder/edge/PonderVotingUserHasQuestionEdgeType.php',
+    'ProjectAddProjectsEmailCommand' => 'applications/project/command/ProjectAddProjectsEmailCommand.php',
     'ProjectBoardTaskCard' => 'applications/project/view/ProjectBoardTaskCard.php',
     'ProjectCanLockProjectsCapability' => 'applications/project/capability/ProjectCanLockProjectsCapability.php',
     'ProjectConduitAPIMethod' => 'applications/project/conduit/ProjectConduitAPIMethod.php',
@@ -6517,6 +6518,7 @@ phutil_register_library_map(array(
     'PonderVoteSaveController' => 'PonderController',
     'PonderVotingUserHasAnswerEdgeType' => 'PhabricatorEdgeType',
     'PonderVotingUserHasQuestionEdgeType' => 'PhabricatorEdgeType',
+    'ProjectAddProjectsEmailCommand' => 'MetaMTAEmailTransactionCommand',
     'ProjectCanLockProjectsCapability' => 'PhabricatorPolicyCapability',
     'ProjectConduitAPIMethod' => 'ConduitAPIMethod',
     'ProjectCreateConduitAPIMethod' => 'ProjectConduitAPIMethod',
diff --git a/src/applications/project/command/ProjectAddProjectsEmailCommand.php b/src/applications/project/command/ProjectAddProjectsEmailCommand.php
new file mode 100644
index 0000000000..dc69b2d208
--- /dev/null
+++ b/src/applications/project/command/ProjectAddProjectsEmailCommand.php
@@ -0,0 +1,70 @@
+<?php
+
+final class ProjectAddProjectsEmailCommand
+  extends MetaMTAEmailTransactionCommand {
+
+  public function getCommand() {
+    return 'projects';
+  }
+
+  public function getCommandSyntax() {
+    return '**!projects** //#project ...//';
+  }
+
+  public function getCommandSummary() {
+    return pht('Add related projects.');
+  }
+
+  public function getCommandDescription() {
+    return pht(
+      'Add one or more projects to the object by listing their hashtags. '.
+      'Separate projects with spaces. For example, use `!projects #ios '.
+      '#feature` to add both related projects.'.
+      "\n\n".
+      'Projects which are invalid or unrecognized will be ignored. This '.
+      'command has no effect if you do not specify any projects.');
+  }
+
+  public function getCommandAliases() {
+    return array(
+      'project',
+    );
+  }
+
+  public function isCommandSupportedForObject(
+    PhabricatorApplicationTransactionInterface $object) {
+    return ($object instanceof PhabricatorProjectInterface);
+  }
+
+  public function buildTransactions(
+    PhabricatorUser $viewer,
+    PhabricatorApplicationTransactionInterface $object,
+    PhabricatorMetaMTAReceivedMail $mail,
+    $command,
+    array $argv) {
+
+    $project_phids = id(new PhabricatorObjectListQuery())
+      ->setViewer($viewer)
+      ->setAllowedTypes(
+        array(
+          PhabricatorProjectProjectPHIDType::TYPECONST,
+        ))
+      ->setObjectList(implode(' ', $argv))
+      ->setAllowPartialResults(true)
+      ->execute();
+
+    $xactions = array();
+
+    $type_project = PhabricatorProjectObjectHasProjectEdgeType::EDGECONST;
+    $xactions[] = $object->getApplicationTransactionTemplate()
+      ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
+      ->setMetadataValue('edge:type', $type_project)
+      ->setNewValue(
+        array(
+          '+' => array_fuse($project_phids),
+        ));
+
+    return $xactions;
+  }
+
+}