SMTP dropped connection

i just replaced a netgear box with an RB532. Is is being used as a broadband router with PPPOE client. As soon as i replaced the firewall my customer started having outgoing SMTP connections dropped just to a select few email domains. The mail server is Masquareded behind the public ip. SMTP nat connections coming in work fine. The problem goes away when we switch back to the original router. I have “accept established” and “accept related” rules placed in the foward chain.

This is a very strainge problem, Any sugestions

Thank you

Sounds like an MTU problem with the PPPoE connection. See the post http://forum.mikrotik.com//viewtopic?t=15122 for a solution.