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!

The whole site in one document for easy reference!
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
SMTP Security Issues
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
SMTP Replies and Reply Codes
Next Topic/Section

SMTP Commands
(Page 2 of 3)

Current SMTP Commands

Table 252 lists the commands currently used in modern SMTP, in the order they are described in RFC 2821, with a brief description of each.


Table 252: SMTP Commands

Command Code

Command

Parameters

Description

HELO

Hello

The domain name of the sender.

The conventional instruction sent by an SMTP sender to an SMTP receiver to initiate the SMTP session.

EHLO

Extended Hello

The domain name of the sender.

Sent by an SMTP sender that supports SMTP extensions to greet an SMTP receiver and ask it to return a list of SMTP extensions the receiver supports. The domain name of the sender is supplied as a parameter.

MAIL

Initiate Mail Transaction

Must include a “FROM:” parameter specifying the originator of the message, and may contain other parameters as well.

Begins a mail transaction from the sender to the receiver.

RCPT

Recipient

Must include a “TO:” parameter specifying the recipient mailbox, and may also incorporate other optional parameters.

Specifies one recipient of the e-mail message being conveyed in the current transaction.

DATA

Mail Message Data

None

Tells the SMTP receiver that the SMTP sender is ready to transmit the e-mail message. The receiver normally replies with an intermediate “go ahead” message, and the sender then transmits the message one line at a time, indicating the end of the message by a single period on a line by itself.

RSET

Reset

None

Aborts a mail transaction in progress. This may be used if an error is received upon issuing a MAIL or RCPT command, if the SMTP sender cannot continue the transfer as a result.

VRFY

Verify

E-mail address of mailbox to be verified.

Asks the SMTP receiver to verify the validity of a mailbox.

EXPN

Expand

E-mail address of mailing list.

Requests that the SMTP server confirm that the address specifies a mailing list, and return a list of the addresses on the list.

HELP

Help

Optional command name.

Requests help information: general help if no parameter is supplied, otherwise information specific to the command code supplied.

NOOP

No Operation

None

Does nothing except for verifying communication with the SMTP receiver.

QUIT

Quit

None

Terminates the SMTP session.


Like FTP commands, SMTP commands are not case sensitive.

Certain SMTP extensions make changes to the basic SMTP command set. For example, the AUTH extension specifies a new command (also called AUTH) that specifies an authentication method the SMTP client wants to use. Other extensions define new parameters for existing commands. For example, the SIZE extension defines a SIZE parameter that can be added to a MAIL command to tell the SMTP receiver the size of the message to be transferred.

Key Concept: The SMTP sender performs operations using a set of SMTP commands. Each command is identifies using a four-letter code. Since SMTP only supports a limited number of functions, it has a small command set.



Previous Topic/Section
SMTP Security Issues
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
SMTP Replies and Reply Codes
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.