You cna alos setup a "catchall" or "default" address and forward it to another address of your choice (or a mailbox in its own right).
So, I create the "catchall" mailbox of [email protected]
I set this as my "catchall" in my Control Panel.
If somebody sends a mail to - anything other than a real [email protected] then it will be routed to the catchall address.
That can be achieved in a number of ways.
If they are seperate linux machines a .forward file in the persons home directory can do the trick
You can create an entry in a forward file for each e-mail address OR you can add a rewrite rule to rewrite earthlink.com to earthlink.net
The exact file and where to make the change , and what to change, depends on what it is you are using as your smtp server (sendmail,exim,etc.)