question about mail

[Vortek, Eater of Souls!]

Hello everyone,
I have a quick question about the mail program.
Yes yes, I know, old, outdated, and practically useless. <smile>
Unfortunately, some of my more...lazy?...users seem to like it.
My question is, how do I get the domain name in outbound mail to say
the-bofh.com, and not valhalla.the-bofh.com when someone writes a new
message.
Although this isn't a problem with my dns setup, I'd just like to have
all emails, wether they be sent from pine, mutt, elm, or whatever, to
have the same domain name.
Mail is the only one I can't get to do this.
Any help would be greatly appriciated.
Thanks.