OK, so maybe the last two are a little bogus :-).
2.5 SENDING E-MAIL TO OTHER NETWORKS
There are a number of computer networks that are not directly part of the Net, but which are now connected through "gateways" that allow the passing of e-mail. Here's a list of some of the larger networks, how to send mail to them and how their users can send mail to you:
America Online
Remove any spaces from a user's name and append "aol.com," to get
user@aol.com
America Online users who want to send mail to you need only put your Net address in the "to:" field before composing a message.
ATTMail
Address your message to user@attmail.com.
From ATTMail, a user would send mail to you in this form: