Simple Mail Transfer Protocol (SMTP)

Simple Mail Transfer Protocol (SMTP) is the standard protocol used to submit and relay email messages.

Format
Email & Communication
Updated
Updated
Glossary Email & Communication
Simple Mail Transfer Protocol Also known as SMTP.Aliases: mail transfer protocol, outgoing mail protocol.

Definition

Simple Mail Transfer Protocol (SMTP) is the standard protocol used to submit and relay email messages.

How it works

SMTP moves mail in two settings: your mail app submits an outgoing message to your provider's server, and servers relay messages between domains — looking up the recipient's MX records to find the next hop. That is the whole job. Reading mail, filtering it, and storing it are other systems' work.

Example: A sending server looks up the recipient domain's MX records before opening an SMTP connection.

Often confused: SMTP delivers mail to the server; IMAP and POP3 are how you get it back out.

Sources

Last reviewed 2026-07-19.