diff --git a/src/applications/auth/controller/PhabricatorAuthOneTimeLoginController.php b/src/applications/auth/controller/PhabricatorAuthOneTimeLoginController.php
--- a/src/applications/auth/controller/PhabricatorAuthOneTimeLoginController.php
+++ b/src/applications/auth/controller/PhabricatorAuthOneTimeLoginController.php
@@ -84,6 +84,22 @@
         ->addCancelButton('/login/email/', pht('Send Another Email'));
     }
 
+    if (!$target_user->canEstablishWebSessions()) {
+      return $this->newDialog()
+        ->setTitle(pht('Unable to Establish Web Session'))
+        ->setShortTitle(pht('Login Failure'))
+        ->appendParagraph(
+          pht(
+            'You are trying to gain access to an account ("%s") that can not '.
+            'establish a web session.',
+            $target_user->getUsername()))
+        ->appendParagraph(
+          pht(
+            'Special users like daemons and mailing lists are not permitted '.
+            'to log in via the web. Log in as a normal user instead.'))
+        ->addCancelButton('/');
+    }
+
     if ($request->isFormPost()) {
       // If we have an email bound into this URI, verify email so that clicking
       // the link in the "Welcome" email is good enough, without requiring users
diff --git a/src/applications/auth/management/PhabricatorAuthManagementRecoverWorkflow.php b/src/applications/auth/management/PhabricatorAuthManagementRecoverWorkflow.php
--- a/src/applications/auth/management/PhabricatorAuthManagementRecoverWorkflow.php
+++ b/src/applications/auth/management/PhabricatorAuthManagementRecoverWorkflow.php
@@ -71,6 +71,16 @@
           $can_recover));
     }
 
+    if (!$user->canEstablishWebSessions()) {
+      throw new PhutilArgumentUsageException(
+        pht(
+          'This account ("%s") can not establish web sessions, so it is '.
+          'not possible to generate a functional recovery link. Special '.
+          'accounts like daemons and mailing lists can not log in via the '.
+          'web UI.',
+          $username));
+    }
+
     $engine = new PhabricatorAuthSessionEngine();
     $onetime_uri = $engine->getOneTimeLoginURI(
       $user,