[Exim] multiple domains and unknown-users

This is a multi-part message in MIME format.
--
[ Picked text/plain from multipart/alternative ]
Hello @all,

I am very new to exim; actually I use postfix and cyrus with a mysql-db
for authentification.

I have a little problem; I would like to host multiple domains at one
server (with one ip-address) - but I would like to have an 'default'
adress for each domain.
For example - I am hosting
domain1.com
domain2.com
Now I get an email 'unknown-user@???' and I would like to
forward this one to an real existing user at domain1.com - the same
thing for domain2.com. Therefore I don't want mails for unknown-users
get forwarded to one global account, but to one account per domain.
If I understand postfix (!) correctly I only can forward mails to
unknown users to an global account.
Therefore I looked for another program.
I have searched the documentation and mailing lists of exim, but
actually didn't found anything.

Another thing is - is it possible to use an mysql-database for
authentification (perhaps via pam) ?

Thank you.
Sebastian

--