Here’s a great article on DKIM:
To quote one of our engineers:
Just an FYI about DKIM – this has matured since we started setting it up for customers a couple of years ago. The software is now “OpenDKIM”, available on the EPEL repository.
There’s a HowTo for setting it up at the URL below. It’s correct, except that it assumes a source install, rather than installing opendkim from yum. The other details are all good and useful (opendkim configuration, postfix integration, DNS setup).
