source: http://www.securityfocus.com/bid/51401/info

MailEnable is prone to a cross-site scripting vulnerability because it fails to properly sanitize user-supplied input.

An attacker may leverage this issue to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site. This may allow the attacker to steal cookie-based authentication credentials and launch other attacks.

The following MailEnable versions are vulnerable:
Professional, Enterprise, and Premium 4.26 and prior versions
Professional, Enterprise, and Premium 5.52 and prior versions
Professional, Enterprise, and Premium 6.02 and prior versions 

http://example.com/mewebmail/Mondo/lang/sys/ForgottenPassword.aspx?Username=[xss]