[Exim] Exim as front door to Exchange

I have recently set up Exim as a front door to Exchange. I have used
some of the how-tos from previous list posts. I have mainly followed
the advice of Tabor Wells, using LDAP lookups. I still think I have some
problems, however.

What do I need to on the Exchange side to get it to accept mail from
Exim? How do I check to see if mail is going to the Exim box? Will it
just stay on the Exim box until it finds a place to go?

Thanks.