User @subdomain.maindomain.com) not listed in Domino Directory

Hi

I can not email from my Notes domain/client to a SMTP server using sub domain - it works fine from other clients and ail systems but it seems like email containing “to my @maindomain.com” and to @subdomain.maindomain.com is not possible - it seems my domino server says everything that contains ´@maindomain is part of our domino directory even though my DNS MX record to the sub domain points to a different mail server and resolves fine, Domino just comes with this error mail message every time

“User @subdomain.maindomain.com) not listed in Domino Directory”

I have setup a Global domain document - to the sub domain and also tried to setup foreign domain… still same error - what can I do in order to send email from Notes to a sub domain?

Thanks