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.