domain name, machine name alias

[Dan McCullough]

I have two machines, the old machine is mail.domain.com and the new
one is mail1.domain.com I need to setup the new machine so that it
will accept incoming mail as if it were mail.domain.com without having
to change settings for all my users.  Is that possible, or is it
easier to just make mail1.domain.com, mail.domain.com and make sure
they arent plugged in at the same time.