Introduction
| Protocol | Port | Description |
|---|---|---|
SMTP | 25 | |
SSL/TLS | 465 | |
StartTLS | 587 |
SMTP Commands
| Command | Description | RFC |
|---|---|---|
HELO | Identifies the sending SMTP server | RFC 5321 |
EHLO | Extended HELO, provides more information | RFC 5321 |
MAIL FROM | Specifies the sender’s email address | RFC 5321 |
RCPT TO | Specifies the recipient’s email address | RFC 5321 |
DATA | Initiates the message data transmission | RFC 5321 |
RSET | Resets the session to initial state | RFC 5321 |
VRFY | Requests verification of an email address | RFC 5321 |
EXPN | Requests the expansion of a mailing list | RFC 5321 |
NOOP | No operation, used for testing or keep-alive | RFC 5321 |
QUIT | Closes the SMTP session | RFC 5321 |
AUTH | Initiates authentication process | RFC 4954 |
STARTTLS | Initiates a secure TLS session | RFC 3207 |
HELP | Requests help information from the server | RFC 5321 |
RFC 821 – Simple Mail Transfer Protocol
Protocol definition for SMTP. This document covers the model, operating procedure, and protocol details for SMTP.
RFC 1869 – SMTP Service Extensions
Definition of the ESMTP extensions for SMTP. This describes a framework for extending SMTP with new commands, supporting dynamic discovery of the commands provided by the server, and defines a few additional commands.
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