This will not work under various circumstances, but I believe that it generally will.
I would try using the Net::Finger module. The documentation at that site is pretty straightforward, so you should have very little problems.
This should work with sites that give the user an account. However, I do not think that it will work with a web-mail account like Yahoo! or Excite. This module queries the server for a user. The server you are using may not have the Net::Finger module. If it doesn't, I would just download the module and modify it for your use. I'd help you more, but I don't know the syntax for a Finger query.

E-mail ( lied5@yahoo.com ) or /msg me if you need any more help
Peace... BlackFlag