[blacky_penguin]

in basic words, your mail server will generate some keys and using those will sign the outgoing mails. Then the receiving side will compare those things with your DNS entries.

Here's some links
http://www.howtoforge.com/how-to-imp...lter-centos5.1
http://antispam.yahoo.com/domainkeys

http://dkim.org/
http://domainkeys.sourceforge.net/