There's nothing to be configured at the moment. Tuomos Cyrus-SASL and Postfix RPMS took care of the most basic needs, when they added a few extra files and directories.
All we need for the moment is to start saslauthd.
[email@example.com]# /etc/init.d/saslauthd start
To check whether and how saslauthd was started we do ps wax | grep saslauthd. This is what you should get:
[firstname.lastname@example.org]# ps wax | grep saslauthd 869 ? S 0:08 /usr/sbin/saslauthd -m /var/run/saslauthd/mux -a shadow
The option -m /var/run/saslauthd/mux tells saslauthd where to create it's socket to listen for connections.
The option -a shadow tells saslauthd which mechanism it should use to authenticate users.
There are so many ways to build and configure SASL and each distribution does it differently. If you use saslauthd check either your init-scripts how they bring up saslauthd and verify that their settings e.g. paths etc. make sense or use the example above.