How Email Works

Have you ever wondered how the messages you send and receive on your desktop computer travel through the Internet? The process is actually very simple. The two basic components of Email transport are Simple Mail Transfer Protocol (SMTP) and Post Office Protocol (POP).

The process of sending and receiving Email is illustrated by this diagram:

Outgoing Mail

When you send an Email message to someone, your Email program (e.g. Eudora) uses SMTP to send the mail to the local SMTP server (e.g. mail.ncifcrf.gov). The server then sends the mail to your addressee's computer, usually by means of the SMTP protocol.

Why doesn't your computer talk directly to your addressee's computer? It would take a lot longer for your mail to leave your PC because it would have to call up each addressee's computer and deliver your mail. Some computers are "hard to find;" it's much better to let another computer "hunt" for your addressee than to make your PC do it. Finally, sometimes your addressee's computer will not be available when you want to send mail. The SMTP server handles this by holding your mail until the other computer is ready to accept it, which eliminates the inconvenience of having unsent messages remaining on your PC.

Incoming Mail

When somebody sends you mail, other computers use the SMTP protocol to deliver the mail to your POP server. Your POP server puts mail in your "mail drop," where it stays until your Email program picks it up. When you check your mail, your Email program uses what is called POP version 3 (POP3) to pick up your mail and move it to your PC.

Why doesn't your Email program use SMTP to receive your Email? SMTP works best when the computers it knows about are always ready for mail. Unless you want to run your Email program 24 hours per day, seven days a week, SMTP wouldn't work very well for you. It also doesn't work very well in lab environments, where you might use any number of different PCs.

Excerpts taken from Eudora Pro v3.0 User Manual © 1996 Qualcomm, Inc.

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