All emails FROM a virtual site? You have no control over how people SEND email; you can't force them to use your server, or any other server for that matter.
- answering a different question, but Earthlink does this:On the ISP level this can be done - Earthlink does it. If you dial into an Earthlink account you are forced to use mail.earthlink.net for your SMTP, POP can be whatever you want. If you use another smtp server, Earthlink, in their infinite wisdom to try and stop SPAM, gives you a 550 error. It is a pain in the ass for customers with legitimate domain names of their own just using Earthlink as their ISP connection.
Just an FYI Jale