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!

Enjoy The TCP/IP Guide? Get the complete PDF!
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 Delivery Protocol: The Simple Mail Transfer Protocol (SMTP)

Previous Topic/Section
TCP/IP Electronic Mail Delivery Protocol: The Simple Mail Transfer Protocol (SMTP)
Previous Page
Pages in Current Topic/Section
1
2
Next Page
SMTP Communication and Message Transport Methods, Client/Server Roles and Terminology
Next Topic/Section

SMTP Overview, History and Standards
(Page 2 of 2)

SMTP Extensions and Revisions

As the 1980s progressed and TCP/IP and the Internet both grew in popularity, SMTP gradually overtook other methods to become the dominant method of e-mail message delivery. For a number of years, the protocol was used mostly “as is”, with no new RFCs published to define new versions or formally change its behavior.

This changed in February 1993, when RFC 1425, SMTP Service Extensions, was published. As the name suggests, this standard describes a process for adding new capabilities to extend how SMTP works, while maintaining backward-compatibility with existing systems. SMTP with these extensions is sometimes called Extended SMTP or ESMTP (though use of this term seems to be not entirely universal). As development of SMTP continued, RFC 1425 was revised in RFC 1651 in July 1994 and then RFC 1869 in November 1995. Along with these, a number of other RFCs defining particular SMTP extensions such as pipelining and message size declaration were defined.

In April 2001, another major milestone in TCP/IP e-mail was reached when revisions of RFC 821 and RFC 822 were published, as RFCs 2821 and 2822 respectively. Both documents are “consolidations” of updates and changes that had been made to RFCs 821 and 822 between 1982 and 2001. And no, I don't think it is a coincidence that the old and new RFC numbers are exactly “2000” apart. RFCs 2820 and 2823 were both published in May 2000, so it looks like 2821 and 2822 were reserved for the e-mail standards. I think this was a great idea, as it makes more clear that the new RFCs are revisions of the old ones.

RFC 2821 is the current base standard for SMTP. It incorporates the base protocol description from RFC 821, and the latest SMTP extensions as defined in RFC 1869. Perhaps more importantly, it updates the description of the e-mail communication model to reflect the realities of modern TCP/IP networks, especially the e-mail features built into the Domain Name System (DNS). We'll examine this in more detail in the next topic.


Previous Topic/Section
TCP/IP Electronic Mail Delivery Protocol: The Simple Mail Transfer Protocol (SMTP)
Previous Page
Pages in Current Topic/Section
1
2
Next Page
SMTP Communication and Message Transport Methods, Client/Server Roles and Terminology
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.