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
@@ -79,6 +79,13 @@
     $tos = $args->getArg('to');
     $ccs = $args->getArg('cc');
 
+    if (!$tos && !$ccs) {
+      throw new PhutilArgumentUsageException(
+        pht(
+          'Specify one or more users to send mail to with `--to` and '.
+          '`--cc`.'));
+    }
+
     $names = array_merge($tos, $ccs);
     $users = id(new PhabricatorPeopleQuery())
       ->setViewer($viewer)
@@ -103,6 +110,10 @@
     }
 
     $subject = $args->getArg('subject');
+    if ($subject === null) {
+      $subject = pht('No Subject');
+    }
+
     $tags = $args->getArg('tag');
     $attach = $args->getArg('attach');
     $is_bulk = $args->getArg('bulk');
@@ -110,7 +121,6 @@
     $console->writeErr("%s\n", pht('Reading message body from stdin...'));
     $body = file_get_contents('php://stdin');
 
-
     $mail = id(new PhabricatorMetaMTAMail())
       ->addTos($tos)
       ->addCCs($ccs)