[cobalt-users] RaQ3 Email errors using External Mail server w/ Virtual sites

["DotCom Production" <ariel@xxxxxxxxxxxxxxxxx>]

I'm a new to this list, so forgive me if this has been asked already. I have
searched the online knowledge base and as much of the list archive as I
could - to no avail.

My company is in the thankless position of migrating AT&T's (former) shared
hosting clients over to their new dedicated RaQ hosting environment. So far,
so good!

The problem I am having is with two virtual sites that need to use an
external IP address ( secondary mail-server) for their MX records. I have
setup the A record for mail.mydomain.com pointing to the correct IP address
and setup the MX record to use mail.mydomain.com. The customer can send mail
with no problem, but replying to their mail or trying to send new mail to
them results in a "550 error <name@xxxxxxxxxxxx>... User unknown."

I have successfully setup and used secondary mail servers many times on the
RaQ 3's, but only on single sites - never on virtual sites.

Any insight / help would be much appreciated.

~Jon