diff --git a/playbooks/roles/mail/templates/oauth2.inc.php.j2 b/playbooks/roles/mail/templates/oauth2.inc.php.j2
index 919e162..2be0888 100644
--- a/playbooks/roles/mail/templates/oauth2.inc.php.j2
+++ b/playbooks/roles/mail/templates/oauth2.inc.php.j2
@@ -17,3 +17,5 @@ $config['oauth_login_redirect'] = false;
 
 $config['force_https'] = true;
 $config['use_https'] = true;
+
+$config['mail_domain'] = '%d';