[Exim] Question re. SMTP Auth

Hi Folks...

Just wondering if anyone could tell me if it's possible (and if so,
how!) to do SMTP plaintext auth from a different password file depending
on which port the connection comes from.

My configuration has users coming in on port 25 to different Ips - it
would be nice to be able to reverse-lookup the IP, and to an lsearch of
a file in a directory like /etc/virtual/mail.domain1.com/smtp-passwd
Or
/etc/virtual/mail.domain2.com/smtp-passwd

And for those domains to have completely separate namespace.

Is it possible?

Thanks,

Neil

Neil S Hamilton, NSH Consultancy