Rockliffe Mailsite versions 6.1.22.1 and below suffer from a directory transversal problem allowing any authenticated user to access any users mailbox with the RENAME command.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/42805/Mailsite-6.1.22.1.txt
Source: https://packetstormsecurity.com/files/42805/Mailsite-6.1.22.1.txt.html