[Exim] mx record

Hi list!

I have a quiestion. Can i config my exim for using more than one
addresses for mailing. The server has a name 1stdomain.foo the
@1stdomain.foo addressing is exist and works.
The 2dndomain.foo (registrated) 'll be use for mailing only.
The entry of the 2nddomain.foo contains /MX 1stdomain.foo -right form/
How can different users use different addresses?
Can Exim do this thing?

Best regards
Gergely Kodaj