I (AGS) am in no way, shape, or form responsible for what you do with the information learned in this instructable; the reason being, in some countries it is illegal to relay emails using SMTP services because more and more servers that have SMTP enabled are being used and abused by spammers to send UBE (Unsolicited Bulk Email ---junk mail) by the thousands.
A little background information:
Back before the days of popular email websites such as Hotmail, Yahoo, and G-mail that gives users a GUI, there was a system called SMTP (Simple Mail Transfer Protocol) that was the primary way to send messages.
This Instructable will show you how to forge e-mails using an SMTP enabled server.
What you will need:
-A SMTP server that allows relaying
-A Windows OS (95/98/NT/ME/XP)
Step 1: Brief Overview of SMTP
NOTE: Although these servers use SMTP you have to be authenticated to actually send anonymous emails. If you don't have an account on the server you will not be able to send fake emails. The reason being? Since spammers have found a way to utilize SMTP to send bulk spam mail, most system administrators have banned anonymous sending of messages from there servers. Sending an anonymous email from inside an SMTP server without having an account is called relaying; and unfortunately as you might find, servers that allow relaying are few and far between.
So how do you find a server that you can use to send anonymous emails? Easy, use the one assigned to you by your Internet service provider. Since it's your providers server it is more than likely that your IP address will be designated a slot that's already authenticated.
However, it is not guaranteed.