diff --git a/src/applications/people/controller/PhabricatorPeopleProfileController.php b/src/applications/people/controller/PhabricatorPeopleProfileController.php
--- a/src/applications/people/controller/PhabricatorPeopleProfileController.php
+++ b/src/applications/people/controller/PhabricatorPeopleProfileController.php
@@ -136,11 +136,14 @@
           ->setWorkflow(true)
           ->setHref($this->getApplicationURI('delete/'.$user->getID().'/')));
 
+      $can_welcome = $user->canEstablishWebSessions();
+
       $actions->addAction(
         id(new PhabricatorActionView())
           ->setIcon('fa-envelope')
           ->setName(pht('Send Welcome Email'))
           ->setWorkflow(true)
+          ->setDisabled(!$can_welcome)
           ->setHref($this->getApplicationURI('welcome/'.$user->getID().'/')));
     }
 
diff --git a/src/applications/people/controller/PhabricatorPeopleWelcomeController.php b/src/applications/people/controller/PhabricatorPeopleWelcomeController.php
--- a/src/applications/people/controller/PhabricatorPeopleWelcomeController.php
+++ b/src/applications/people/controller/PhabricatorPeopleWelcomeController.php
@@ -3,19 +3,12 @@
 final class PhabricatorPeopleWelcomeController
   extends PhabricatorPeopleController {
 
-  private $id;
-
-  public function willProcessRequest(array $data) {
-    $this->id = $data['id'];
-  }
-
-  public function processRequest() {
-    $request = $this->getRequest();
-    $admin = $request->getUser();
+  public function handleRequest(AphrontRequest $request) {
+    $admin = $this->getViewer();
 
     $user = id(new PhabricatorPeopleQuery())
       ->setViewer($admin)
-      ->withIDs(array($this->id))
+      ->withIDs(array($request->getURIData('id')))
       ->executeOne();
     if (!$user) {
       return new Aphront404Response();
@@ -23,6 +16,18 @@
 
     $profile_uri = '/p/'.$user->getUsername().'/';
 
+    if (!$user->canEstablishWebSessions()) {
+      return $this->newDialog()
+        ->setTitle(pht('Not a Normal User'))
+        ->appendParagraph(
+          pht(
+            'You can not send this user a welcome mail because they are not '.
+            'a normal user and can not log in to the web interface. Special '.
+            'users (like bots and mailing lists) are unable to establish web '.
+            'sessions.'))
+        ->addCancelButton($profile_uri, pht('Done'));
+    }
+
     if ($request->isFormPost()) {
       $user->sendWelcomeEmail($admin);
       return id(new AphrontRedirectResponse())->setURI($profile_uri);
diff --git a/src/applications/people/storage/PhabricatorUser.php b/src/applications/people/storage/PhabricatorUser.php
--- a/src/applications/people/storage/PhabricatorUser.php
+++ b/src/applications/people/storage/PhabricatorUser.php
@@ -587,6 +587,13 @@
   }
 
   public function sendWelcomeEmail(PhabricatorUser $admin) {
+    if (!$this->canEstablishWebSessions()) {
+      throw new Exception(
+        pht(
+          'Can not send welcome mail to users who can not establish '.
+          'web sessions!'));
+    }
+
     $admin_username = $admin->getUserName();
     $admin_realname = $admin->getRealName();
     $user_username = $this->getUserName();