Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Searchable, convenient, complete TCP/IP information.
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)
                     9  TCP/IP Electronic Mail System Overview and Concepts

Previous Topic/Section
TCP/IP Electronic Mail System Overview and Concepts
Previous Page
Pages in Current Topic/Section
12
3
Next Page
TCP/IP Electronic Mail Communication Overview: Message Composition, Submission, Delivery, Receipt, Processing and Access
Next Topic/Section

TCP/IP Electronic Mail System Overview and History
(Page 3 of 3)

Overview of the TCP/IP Electronic Mail System

One of the most important general concepts in the modern electronic mail system is that a distinction is made between protocols that deliver electronic mail between SMTP hosts on the internetwork, and those that let users access received mail on their local hosts. To continue our analogy, different protocols are used for sending mail between post offices, and for “home delivery”. As we'll see, this was done intentionally, to make it possible to send mail to users even if they are not connected to the Internet at the time mail was sent. This decoupling is critical as it enables delayed communication, where mail can be sent when the sender wants to transmit it, and received when the recipient wants to read it.

Over the years, the basic components defined in the early 1980s have not changed substantially, but how they are used has evolved and been improved. Early electronic mail delivery involved the use of route specifications by one SMTP host to dictate how mail was to be delivered through intermediate systems; today, the Domain Name System makes much of that obsolete, facilitating nearly immediate direct mail delivery in most cases. Early electronic mail supported only simple text, where we can now send graphical images, programs and other files in e-mail. Modern high-speed Internet connections and updated access protocols allow modern e-mail to be the realization of the ultimate goal of nearly instantaneous communication even across continents.

Key Concept: One of the most important TCP/IP applications is the internetworking equivalent of the real-world postal delivery system, commonly called electronic mail or e-mail. The history of e-mail goes back to the very earliest days of TCP/IP’s development; today it is used by millions of people every day to send both simple and complex messages around the world. TCP/IP e-mail is not a single application, but rather a complete system that includes several protocols, software elements and components.



Previous Topic/Section
TCP/IP Electronic Mail System Overview and Concepts
Previous Page
Pages in Current Topic/Section
12
3
Next Page
TCP/IP Electronic Mail Communication Overview: Message Composition, Submission, Delivery, Receipt, Processing and Access
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.