diff --git a/imap.php b/imap.php
index 5f88848..ed55a4a 100644
--- a/imap.php
+++ b/imap.php
@@ -63,6 +63,9 @@ class imap
       {
         // imap_errors() takes the errors and clear the error stack
         $errors = imap_errors();
+        if (substr ($e->getMessage (), 0, 35) ===
+            "Can not authenticate to IMAP server")
+          throw new Exception ("IMAP error : ".$e->getMessage(), 401);
         throw new Exception ("IMAP error : ".$e->getMessage(), 500);
       }
     }