[Exim] Setting up a backup mail server?

This has been asked before but I could not find any answers.

I'm looking to set up a two-mail-server system where both servers hold and
receive the mail for a single domain. Both servers are to hold exactly the
same mail, so that each message sent to the domain would wind up on both
servers. What I want is for both servers to be MXs of the domain, and for
one server to, in addition to performing local delivery when e-mail is
received, automatically send the e-mail to the other.

Is there any way to do this? I'm confused by Exim configuration, so I
figured I'd better ask. Please cc all replies to me.

Thanks,

I-Gene Leong
ileong@???