Email: Messages sent across a network from one user to another


E-mail refers to messages, most often text, sent across a network from one user to one or more users. On the Internet, e-mail is usually accomplished through the use of two protocols, SMTP and POP3.

SMTP, which stands for Simple Mail Transfer Protocol, is used by the program that sends the message. POP3 is the third version of a protocol called POP, or Post Office Protocol, and is used by the program that receives the message. In addition to receiving the message, the POP3 program is responsible for storing it until the user actually retrieves it on his or her computer.

The SMTP and POP3 programs don't reside on the computers of the users who compose and receive the mail. Instead, each user is given an account on an SMTP or POP3 server provided by the user's ISP. If you look under the setup options of any e-mail client, such as Outlook, you will see where the domains of the SMTP and POP3 servers are specified. Often, the domains have names like smtp.myISP.com, or mail.myISP.com, where "myISP" is the user's ISP.

When a user sends an e-mail, a chain of events takes place. The user's e-mail client communicates with the user's designated SMTP server. The SMTP program locates the IP address of the e-mail's recipient using a DNS server and then sends the e-mail to the POP3 server at that address. The POP3 server receives the message and then stores it on the server. Eventually, the recipient checks his or her e-mail using an e-mail client, and the POP3 server sends the message to that user, erasing its copy.

This mechanism may seem to have more steps and computers involved than is necessary, but e-mail would not work as well as it does without it. Because the POP3 program is on a server that is always running, a user's account can receive an e-mail at any time. If the POP3 program were on the recipient's computer, that user could only receive e-mail when the computer was on. At any other time, attempts to send e-mail to that user would fail.

When an e-mail fails to reach its destination, it's known as a bounce, because one of the mail servers usually returns the e-mail to the original sender with an explanation. Bounced e-mails are why the SMTP program must be on its own always-running server too. Because of transient problems in the Internet, a valid e-mail address may be temporarily unavailable.

The SMTP server can retry a troublesome e-mail several times before calling it quits. Even after a sender has shut down his or her computer, the SMTP server may still be trying to send out the user's last batch of e-mails.

E-mail is a very inexpensive way to communicate, but like all good things, it can be abused. The most common abuse is spam, unsolicited e-mail messages that are usually commercial in nature and sent in bulk to multiple addresses. Spammers harvest valid e-mail addresses from various sources, or even pay legitimate companies for their customer mailing lists. Spammers also "guess" e-mail addresses, appending randomly generated names to known domain names. The spam itself is usually an offer to buy some dubious (or even illegal) product or service.

Spam is an increasing problem. Once enough spammers begin sending to a particular address, the spam will crowd out the real e-mail, making the account almost useless. To protect themselves, users must be very careful about whom they release their addresses to, and they need to use filters designed to delete spam before it hits the user's in-box. Still, no method is completely effective. The only way spam will go away is if no user ever responds to it, which would make it unprofitable for the spammers to send it.

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This article was sent to us by: Kellan P. Bailey at 02132011

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