ArGoSoft Mail Server 1.8.1.7 and earlier allows a webmail user to cause a denial of service (CPU consumption) by forwarding the email to the user while autoresponse is enabled, which creates an infinite loop.
http://www.iss.net/security_center/static/9759.php
http://archives.neohapsis.com/archives/bugtraq/2002-07/0515.html