SMTP Commands Reference

Reference: SMTP Commands Reference

HELO (Hello)The client sends this command to the SMTP server to identify itself and initiate the SMTP conversation. The domain name or IP address of the SMTP client is usually sent as an argument together with the command (e.g. “HELO client.example.com”). If a domain name is used as an argument with the HELO command, it must be a fully qualified domain name (also called FQDN). 
MAIL FROMSpecifies the e-mail address of the sender. This command also tells the SMTP server that a new mail transaction is starting and makes the server to reset all its state tables and buffers etc. This command is usually sent as the first command after the identifying and login process. If the senders e-mail address is accepted the server will reply with a 250 OK reply code. Example: 

C: MAIL FROM:<mail@samlogic.com> S: 250 OK

 RCPT TO (Recipient To)Specifies the e-mail address of the recipient. This command can be repeated multiple times for a given e-mail message in order to deliver a single e-mail message to multiple recipients. The example below shows how this command can be used to send same e-mail message to two recipients: 

C: MAIL FROM:<mail@samlogic.com> S: 250 OK C: RCPT TO:<john@mail.com> S: 250 OK C: RCPT TO:<peggy@mail.com> S: 250 OK

 
DATAThe DATA command starts the transfer of the message contents (body text, attachments etc). After that the DATA command has been sent to the server from the client, the server will respond with a 354 reply code. After that, the message contents can be transferred to the server. When all message contents have been sent, a single dot (“.”) must be sent in a line by itself. If the message is accepted for delivery, the SMTP server will response with a 250 reply code. Example (the message contents is set to italic in the example below): 

C: DATA S: 354 Send message content; end with <CRLF>.<CRLF> C: Date: Thu, 21 May 2008 05:33:29 -0700 C: From: SamLogic <mail@samlogic.com> C: Subject: The Next Meeting C: To: john@mail.com C: C: Hi John, C: The next meeting will be on Friday. C: /Anna. C: . S: 250 OK

 RSET (Reset)If the RSET command is sent to the e-mail server the current mail transaction will be aborted. The connection will not be closed (this is reserved for the QUIT command, see below) but all information about the sender, recipients and e-mail data will be removed and buffers and state tables will be cleared. VRFY (Verify)This command asks the server to confirm that a specified user name or mailbox is valid (exists). If the user name is asked, the full name of the user and the fully specified mailbox are returned. In some e-mail servers the VRFY command is ignored because it can be a security hole. The command can be used to probe for login names on servers. Servers that ignore the VRFY command will usually send some kind of reply, but they will not send the information that the client asked for. NOOP (No operation)The NOOP command does nothing else than makes the receiver to send an OK reply. The main purpose is to check that the server is still connected and is able to communicate with the client.  QUITAsks the server to close the connection. If the connection can be closed the servers replies with a 221 numerical code and then is the session closed.