What Is SMTP?
- Short Definition:
- SMTP or Simple Mail Transfer Protocol is a TCP/IP protocol used in sending and receiving e-mail.
- Extended Definition:
- Simple Mail Transfer Protocol, abbreviated as SMTP, is an Internet standard communication protocol used for e-mail communications.
A Simple Mail Transfer Protocol is typically used with POP3 or Internet Message Access Protocol to save messages in a server mailbox and download them periodically from the server for the user. SMTP is also used to prevent abuse with the relay of unsolicited messages over e-mail, such as SPAM. That is achieved with the protocol having specific methods and rules configured for relaying mail messages and authenticating users.
SMTP is a text-based protocol which is also connection-focused where a mail sender writes with a mail receiver by issuing command strings. Such communication is called a session, and a single session may have no or many SMTP transactions. An SMTP transaction consists of three command sequences:
- MAIL command, to establish the return address, also called return-path.
- RCPT command, to establish a recipient of the message.
- DATA to signal the beginning of the message text and the content of the message.
Note that SMTP is a delivery protocol only.
For more definitions, check out our dedicated Definitions List.