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!

Read offline with no ads or diagram watermarks!
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 Message Formats and Message Processing: RFC 822 and MIME
                          9  TCP/IP Electronic Mail Standard Message Format: RFC 822

Previous Topic/Section
TCP/IP Electronic Mail RFC 822 Standard Message Format Overview, Structure and General Formatting Rules
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
TCP/IP Electronic Mail RFC 822 Standard Message Format Processing and Interpretation
Next Topic/Section

TCP/IP Electronic Mail RFC 822 Standard Message Format Header Field Definitions and Groups
(Page 2 of 3)

Header Field Groups

The RFC 822 message format specifies many types of headers that can be included in e-mail messages. A small number of headers are mandatory, meaning they must be included in all messages. Some are not mandatory but are usually present, because they are fundamental to describing the message. Others are optional and are included only when needed.

To help organize the many headers, the RFC 2822 standard categorizes them into header field groups (as did RFC 822, though the groups are a little different in the older standard):

  • Origination Date Field: Specifies the date and time that the message was made ready for delivery; see below for details. (This field is in its own group for reasons that are unclear to me; perhaps just because it is important.)

  • Originator Fields: Contain information about the sender of the message.

  • Destination Address Fields: Specify the recipient(s) of the message, which may be in one of three different recipient classes.

  • Identification Fields: Contain information to help identify the message.

  • Informational Fields: Contain optional information to help make more clear to the recipient what the message is about.

  • Resent Fields: Used to preserve the original originator, destination and other fields when a message is resent.

  • Trace Fields: Used to show the path taken by mail as it was transported.

In addition, the format allows other, user-defined fields to be specified, as long as they correspond to the standard “<header name>: <header value>” syntax. This can be used to provide additional information of various sorts. For example, sometimes the e-mail client software will include a header line indicating the name and version of the software used to compose and send the message. We'll also see that MIME uses new header lines to encode information about MIME messages.

Key Concept: Each RFC 822 message begins with a set of headers that carry essential information about the message. These headers are used to manage how the message is processed and interpreted, and also describe the contents of the message body. Each header consists of a header name and a header value. There are over a dozen different standard RFC 822 headers, which are organized into groups; it is also possible for customized user headers to be defined.



Previous Topic/Section
TCP/IP Electronic Mail RFC 822 Standard Message Format Overview, Structure and General Formatting Rules
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
TCP/IP Electronic Mail RFC 822 Standard Message Format Processing and Interpretation
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.