way for postfix to restrict users to certain domains?

["Forrest English" <forrest@truffula.net>]

is there a way to limit which users can use which outgoing domain names
in their mail account?	 and incoming for that matter.

for instance, currently i've got...

truffula.net
madronepress.com

now, i can send mail to any user on my system, at either address, and
they at will can use either address. i'm mostly fine with this except
that one of those is a company site i host.

so, is there a way to say

bob, can only use truffula.net
sally, can only use madronpress.com
joe however, is special and can use both.

any suggestions?

-- 
Forrest English
http://truffula.net

"When we have nothing left to give
There will be no reason for us to live
But when we have nothing left to lose
You will have nothing left to use"
	-Fugazi