[Exim] Exim configuration

Hello again,

I'm still learning alot about exim so fogive me my stupid questions. I have
a questoin which I don't want to have answered here, I just hope someone can
push me into some directions.

We have a system with two domains.

A.com B.com

A.com has all localusers. So normal system users.

B.com has usernames specified in a plain asci file called 'B.com' :

name:pass
othername:otherpass

I want to check wheter the domain name of an incomming mail is B.com and
then search the name in the file.
And append the data to

/var/spool/mail/${local_part}-${domain}

This is the first step I think but I have not really a clue how to start
making this ;(

I think I need a smartuser director first of all?


Thx for any replies.

Elm