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 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
TCP/IP Electronic Mail RFC 822 Standard Message Format Overview, Structure and General Formatting Rules
(Page 3 of 3)
The RFC 822 message always starts
with a set of header fields as described above; the
next topic describes them in more detail.
After all the headers, an empty line must occur. This consists simply
of the characters CRLF by themselves, immediately following
the CRLF at the end of the final header field line. Seeing
two CRLF character pairs in sequence tells the device reading
the message that the end of the headers have been reached. All the remaining
lines are considered the body of the message. Like the header lines,
body lines are comprised of ASCII text and must be no more than 998
characters, with 78 characters or less recommended (for easier reading
on standard 80-character terminal displays).
Since both the header and body of
e-mail messages are simply ASCII text, this means the entire message
is just a text file. This makes these messages very readable, as I said
above, and also quite easy to create. One can use a simple text editor
to create a complete electronic mail message, including headers, and
can read it with a simple text display utility. This contributes to
e-mail's universal appeal.
The drawback is that the decision
to make messages entirely ASCII means there is no native support in
RFC 822 messages for anything that requires more complex structuring,
or that cannot be expressed using the small number of ASCII characters.
One cannot express pictures, or binary files, spreadsheets, sound clips
and so forth directly using ASCII. Also, the use of ASCII makes RFC
822 well-suited to expressing messages in English, but not in many other
languages, which use characters that ASCII cannot represent. All of
these limitations eventually prompted the creation of the enhanced MIME
Key Concept: To ensure that every device on a TCP/IP internetwork can read e-mail sent by every other device, all messages are required to adhere to a specific structure. The standard that first specified the form of modern TCP/IP e-mail messages was RFC 822, and as a result, this is now called the RFC 822 message format. An RFC 822 message consist of a set of message headers and a message body, which are separated by a blank line. RFC 822 messages must contain only plain ASCII text characters; each line must be no more than 1000 characters in length, and the last two characters must be the ASCII characters CR and LF to mark the end of the line.
|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!|
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.