https://github.com/roundcube/roundcubemail/issues/5336

Index: dovecot_ident.php
--- dovecot_ident.php.orig
+++ dovecot_ident.php
@@ -17,8 +17,7 @@ class dovecot_ident extends rcube_plugin 
 
   function add_ident($args)
   {
-    $args['ident'] = $args['ident'] ? array_merge($args['ident'], array('x-originating-ip' => $_SERVER['REMOTE_ADDR']))
-									: array('x-originating-ip' => $_SERVER['REMOTE_ADDR']);
+    $args['preauth_ident'] = array_key_exists('preauth_ident',$args) ? array_merge($args['preauth_ident'], array('x-originating-ip' => $_SERVER['REMOTE_ADDR'])) : array('x-originating-ip' => $_SERVER['REMOTE_ADDR']);
     return $args;
   }
 }