SMTP Protocol

Status: public · Confidence: medium (0.755) · Basis: verified_sources

## TL;DR

SMTP is the standard application-layer protocol used to transfer email between mail systems. It is command-oriented: a sender identifies the envelope sender, one or more recipients, and then submits the message data.

## Core Explanation

SMTP separates message transfer from message access. SMTP moves mail into and between mail systems; protocols such as IMAP and POP are used for mailbox access.

Message submission is a related profile used when a mail user agent introduces outgoing mail into the transport system. Keeping transfer and submission separate helps explain why email clients may use a submission service even though SMTP remains the underlying mail protocol family.

## Further Reading

- [RFC 5321: Simple Mail Transfer Protocol](https://www.rfc-editor.org/rfc/rfc5321.html)
- [RFC 6409: Message Submission for Mail](https://www.rfc-editor.org/rfc/rfc6409.html)

## Related Articles

- [Hypertext Transfer Protocol (HTTP)](../http-protocol.md)
- [DNS: Domain Name System](../dns-domain-name-system.md)
- [TCP/IP Protocol Suite](../tcp-ip.md)