[Exim] envelope rewriting clarification

My users asked me to provide a service like this:

anything@???

is rewritten as user@???

There are cname records for all the
hosts, and these are all listed as
local domains. I don't think that one can have an MX record
for a cname entry (???)

I've used the smartlist driver as recomended in the FAQ.

At any rate, when a user tries to send a
message from a remote host to the exim installation
here, it appears that the

anything@???

gets rewritten as

anything@???

which gets rewritten as

aname@???


Is this what should happen? What can I do to get
the behaviour I want?

Note that on this machine, without having to do the
lookup, the address is rewritten fine.

--
Dan Kappus, who likes kids, but wouldn't want to eat one