We do this with Microsofts free log parser component and a vbs script. We use IMAIL as out oubound mail server. We spent some time figuring out how to positively identify outgoing email in the logs and then we used the Log Parser component and WSH scripts to periodically go parse the daily log file and extract 'FROM | TO' pairs and then append them to the autowhitlistdelivery.txt file in the proper format.

We also do some dupe checking and sanity checking before appending. If you go google Microsoft Log Parser you'll find it.

Took a bit of time to learn how log parser works and a lot of trial and error building the script, but sweat equity I got plenty of, money I don't.