poprelayd script before 2.0 in Cobalt RaQ3 servers allows remote attackers to bypass authentication for relaying by causing a "POP login by user" string that includes the attacker's IP address to be injected into the maillog log file.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6806
http://archives.neohapsis.com/archives/bugtraq/2001-07/0150.html