[jaxisland]

So I need to setup a domain trust between two different domains, in 2 seperate locations. We have a site to site vpn between them so we are always connected. The first step is to in DNS to create a forwarder to the other domain, if this is not in place you cannot setup the trust.
Now when I create the forwarders on each domain dns server, the mail from site A stops being delivered to site B. But site B can still email to site A. If I remove the forwarders and wait a little bit email comes back. Ive repeated this process about 4 times and each time with the forwarder mail stops, forwarder removed, mail flows.

So, what could be the cause or where should I look to try and resolve this, I am sort of at a loss.

Thanks for the help.