The WrongMX Plugin
Code updated May 3, 2005
WrongMX determines if an email was sent to a lower preference MX when a higher preference MX was likely available.
Add the following files to your local configuration directory (usually /etc/mail/spamassassin):
For Apache SpamAssassin 3.x.x:
How To Use It
Save the two files above in your local configuration directory (/etc/mail/spamassassin/) and set the score in wrongmx.cf to whatever you desire, based on your confidence in your primary MX server stability.
How NOT To Use It
Do not use this plugin on overloaded mail systems that frequently stop accepting connections on the primary MX servers due to system load since it will cause some false positives if you set the score too high.