Use the logterse and other files located here, as they are specific to SME:
http://mirror.contribs.org/smeserver/contribs/bread/mailstats/The instructions are there as well.
Once logterse is installed, as new mail comes in, you should see lines added to the /var/log/qpsmtpd/current file that say 'logterse plugin:' followed by info about the email. (scroll to the bottom of the file to see new entries)
Theres no need to run the multilog stuff.
By the way, there are two forms of Bayes - one you have to teach, and one that learns spam automatically. LearnAsSpam.pl needs users to put all their spam into a folder named LearnAsSpam that you create for each user in /home/e-smith/files/users/<username> .
Then they have to connect to SME and manage it using IMAP, (if they use a client like Outlook) or using a browser and SME webmail/Horde.
IMAP is a bit more trouble than pop3. You'll have to set it up for users, show them how to use it and where to place the spam. I use both types of Bayes, but for customers who arent as likely to want to mess with their email that much, I use the automatic form of Bayes, rather than LearnAsSpam.pl