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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)
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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.
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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.
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RSET
|
Reset
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None
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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.
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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.
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QUIT
|
Quit
|
None
|
Terminates the SMTP session.
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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. |
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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.
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