Linux, mySQL and e-mail server question

This is a general question, mainly because I
don't know what to search for to do what I want...

I have a dedicated web server running Fedora 5
that has a exim mail server running, as well as
a mysql 4.1.22 database.  Basically, I would like
to have a daemon running that logs all incoming
and outgoing e-mail into the database.  Well, not
all e-mail, just e-mails from previous or current
clients.  The flow of this program would be something
like this:

- Detect that an e-mail has been received.
- Check the database to see if a client exists with
  that e-mail, and if there is one, then insert a row
  into the database containing the message of the text
  and other info.

Any ideas?  Ideally, there is some event that I can
catch (i.e., when an e-mail is sent or received through
the mail server) that will let me run an external program
when said event happens.  For example:

onReceiveEmail || onSentEmail: php /my/email/handing/script.php

Is this possible?  Any information would be useful.
Thanks in advance,