# 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.