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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.
Support HackTricks and get benefits!
- Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
- Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
- Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
- **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
- **Share your hacking tricks by submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**