Rockliffe Mailsite versions 7.0.3.1 and below allow remote username enumeration.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/42806/Mailsite-7.0.3.1.txt
Source: https://packetstormsecurity.com/files/42806/Mailsite-7.0.3.1.txt.html