Exchange Server 2003 - multiple email domains

Not sure if theres any Exchange techs still on this forum, but here goes.

My setup is that over time, the company has bought up additional companies. Each of them has kept their identity, webspace and email.

ie [email protected] & [email protected]

I am going from a SBS system that picks up POP3 from an ISP to Exchange 2003 SMTP.

I am able to send emails internally between the 2 company names. both can send emails to the outside world. I am currently not receiving emails from the outside.
my ISP has the MX records to both email domains.

Basically, do I need to add MX records on my internal DNS, do I need to add both domains to my Virtual SMT servers in exchange?

thanks for any pointers.

MX records should be OK as is. Have you configured your router for the proper port setup?

The ISP has to make the MX records point to your Exchange server's public IP address, if they haven't already. Your internal DNS doesn't need MX records though.

You'll also need to tell Exchange to accept mail for those domains, although it sounds like that's already happened. Unfortunately I'm still getting my head around Exchange 2007; I never used 2003 in a real system.

It looks like the router was mishandling SMTP.
after resetting the router and recreating its rules, I am back in business.

Thanks.