diff --git a/lib/kolab_sync_message.php b/lib/kolab_sync_message.php
--- a/lib/kolab_sync_message.php
+++ b/lib/kolab_sync_message.php
@@ -212,9 +212,6 @@
             $headers['To'] = 'undisclosed-recipients:;';
         }
 
-        // remove Bcc header
-        unset($smtp_headers['Bcc']);
-
         // send message
         if (!is_object($rcube->smtp)) {
             $rcube->smtp_init(true);