SMTP and NAT hang

[Josh Pennell <joshp_(_at_)_ioactive_(_dot_)_com>]

Hello fellow bsd'rs,

I recently deployed an oBSD firewall/nat for a medium sized institution.
Everything worked beautifully as usual but there was one hang up.

It seems if there is an out going smtp connection to server mail.foo.com
from behind the nat there is a substantial hang before the mail server
sends back it's header.  Every other outgoing protocal is fast besides
smtp.

So the question is the mail server trying to do a reverse host look up  on
the connecting box and the nat starts to hang the server?  If so is there
something I need to do in the nat rules to compensate for this?

Thanks for your help / time.


Josh