GEN:SID 1:567
Message POLICY SMTP relaying denied
Summary This event is generated when a failed attempt is made to use a Simple Mail Transfer Protocol (SMTP) server to relay mail to a third party.
Impact Rejected of unauthorized use.  This event indicates that an SMTP server is properly configured to reject mail relay attempts.

Detailed Information An attacker may attempt to use an improperly configured SMTP server to relay mail, reflecting the origin of the mail to be the relay SMTP server instead of the actual sender.  A poorly configured SMTP server may be used to relay spam and other undesirable mail.  If an SMTP server rejects relay attempts, it will return an error message indicating the failure.  
Affected Systems SMTP servers
Attack Scenarios An attacker may attempt to relay mail through an improperly configured SMTP server.
Ease of Attack Simple
Corrective Action Configure an SMTP server to reject relayed mail.
Additional References Arachnids
http://www.whitehats.com/info/IDS249

Miscellaneous
http://mail-abuse.org/tsi/ar-fix.html
Rule References arachnids: 249
url: mail-abuse.org/tsi/ar-fix.html