This is an old revision of the document!

“greylisting”

IN MX 5 spamvoid.aufbix.org. IN MX 10 your.real.mx.server IN MX 15 spamvoid.aufbix.org.

Most spam/viruses will hit primary and backup MX server with lower priority. Spamvoid.aufbix.org points to a VALID IP, but connections on port 25/tcp (smtp) will (and must) timeout.