Axway Secure Messenger before 6.5 Updated Release 7, as used in Axway Email Firewall, provides different responses to authentication requests depending on whether the user exists, which allows remote attackers to enumerate users via a series of requests.
https://exchange.xforce.ibmcloud.com/vulnerabilities/81388
http://www.securityfocus.com/bid/57457
http://archives.neohapsis.com/archives/bugtraq/2013-01/0076.html