What does the acronym SMTP stand for in email protocols?

SMTP stands for Simple Mail Transfer Protocol, the standard protocol used to transmit email between mail systems.

SMTP is a push-oriented delivery protocol. An email client submits an outgoing message to a mail server, and mail transfer agents use SMTP to relay it toward the recipient’s domain. The receiving server commonly determines the destination through the domain’s DNS MX record. SMTP defines the transport conversation and envelope information, while the message’s headers and body are specified by separate Internet mail-format standards.

A basic SMTP transaction uses `MAIL FROM` to identify the envelope sender, one or more `RCPT TO` commands for recipients, and `DATA` to transfer the message content. SMTP traditionally uses TCP port 25 for server-to-server relay; authenticated client submission commonly uses ports 587 or 465, depending on the security setup.

SMTP is not normally the protocol used to read stored mail. IMAP and POP are retrieval protocols. Modern SMTP deployments also use extensions such as authentication, STARTTLS encryption, MIME-related capabilities, and SMTPUTF8 for internationalized addresses.