[cobalt-users] email to multiple domains on same IP

["Mike Hart, Julian Web" <mhart@xxxxxxxxxxxxx>]

I have a number of clients who have multiple domains, They want to 
have all of the email default their main address, with numerous 
users.
ie:
joe@xxxxxxxxxxx would be the same as joe@xxxxxxxxxxxx or 
joe@xxxxxxxxx and all delivered to the sixpack.com mail server

i was made to believe that by simply pointing the main dns record 
at the IP address this would occur, bad tech support again?(not 
from Cobalt)  do I need to also set these domains up on the Cobalt 
boxes DNS so they point to the IP? there by being in the main 
email relay list? can i just add them to the list.... do i create 
separate a records for each and default the mailserver as the main 
domains mail server?

I am so confussed...... 

Michael Hart