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# SMTP - Commands
**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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