SMTP Commands Part # 1- List of SMTP Commands


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SMTP Commands Part # 1- List of SMTP Commands

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Please find the list of SMTP commands and its definitions, which can be used on multiple places. For example it can be used to check event SMTP sinks by sending mails.

SMTP commands

SMTP command

Command function

HELO

Sent by a client to identify itself, usually with a domain name.

EHLO

Enables the server to identify its support for Extended Simple Mail Transfer Protocol (ESMTP) commands.

MAIL FROM

Identifies the sender of the message; used in the form MAIL FROM:.

RCPT TO

Identifies the message recipients; used in the form RCPT TO:.

TURN

Allows the client and server to switch roles and send mail in the reverse direction without having to establish a new connection.

ATRN

The ATRN (Authenticated TURN) command optionally takes one or more domains as a parameter. The ATRN command must be rejected if the session has not been authenticated.

SIZE

Provides a mechanism by which the SMTP server can indicate the maximum size message supported. Compliant servers must provide size extensions to indicate the maximum size message that can be accepted. Clients should not send messages that are larger than the size indicated by the server.

ETRN

An extension of SMTP. ETRN is sent by an SMTP server to request that another server send any e-mail messages that it has.

PIPELINING

Provides the ability to send a stream of commands without waiting for a response after each command.

CHUNKING

An ESMTP command that replaces the DATA command. So that the SMTP host does not have to continuously scan for the end of the data, this command sends a BDAT command with an argument that contains the total number of bytes in a message. The receiving server counts the bytes in the message and, when the message size equals the value sent by the BDAT command, the server assumes it has received all of the message data.

DATA

Sent by a client to initiate the transfer of message content.

DSN

An ESMTP command that enables delivery status notifications.

RSET

Nullifies the entire message transaction and resets the buffer.

VRFY

Verifies that a mailbox is available for message delivery; for example, vrfy ted verifies that a mailbox for Ted resides on the local server. This command is off by default in Exchange implementations.

HELP

Returns a list of commands that are supported by the SMTP service.

QUIT

Terminates the session.

The following table lists the extended SMTP commands that Exchange makes available to the SMTP service.

Extended SMTP commands

Extended SMTP command

Command function

X-EXPS GSSAPI

A method that is used by Microsoft Exchange Server 2003 and Exchange 2000 Server servers to authenticate.

X-EXPS=LOGIN

A method that is used by Exchange 2000 and Exchange 2003 servers to authenticate.

X-EXCH50

Provides the ability to propagate message properties during server-to-server communication.

X-LINK2STATE

Adds support for link state routing in Exchange.

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