hacktricks/network-services-pentesting/pentesting-smtp/smtp-commands.md

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**Extracted from:** [**https://serversmtp.com/smtp-commands/**](https://serversmtp.com/smtp-commands/)

**HELO**\
It’s the first SMTP command: is starts the conversation identifying the sender server and is generally followed by its domain name.

**EHLO**\
An alternative command to start the conversation, underlying that the server is using the Extended SMTP protocol.

**MAIL FROM**\
With this SMTP command the operations begin: the sender states the source email address in the “From” field and actually starts the email transfer.

**RCPT TO**\
It identifies the recipient of the email; if there are more than one, the command is simply repeated address by address.

**SIZE**\
This SMTP command informs the remote server about the estimated size (in terms of bytes) of the attached email. It can also be used to report the maximum size of a message to be accepted by the server.

**DATA**\
With the DATA command the email content begins to be transferred; it’s generally followed by a 354 reply code given by the server, giving the permission to start the actual transmission.

**VRFY**\
The server is asked to verify whether a particular email address or username actually exists.

**TURN**\
This command is used to invert roles between the client and the server, without the need to run a new connaction.

**AUTH**\
With the AUTH command, the client authenticates itself to the server, giving its username and password. It’s another layer of security to guarantee a proper transmission.

**RSET**\
It communicates the server that the ongoing email transmission is going to be terminated, though the SMTP conversation won’t be closed (like in the case of QUIT).

**EXPN**\
This SMTP command asks for a confirmation about the identification of a mailing list.

**HELP**\
It’s a client’s request for some information that can be useful for the a successful transfer of the email.

**QUIT**\
It terminates the SMTP conversation.


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