Email Tutorials - Herong's Tutorial Examples - v1.03, by Herong Yang
What Is POP3
This section provides a quick introduction on POP (Post Office Protocol 3) for retrieving email messages. A POP3 sample session of retrieving an email message using the 'telnet' command is included.
What Is POP3? - POP3 (Post Office Protocol 3) is the 3rd version of the POP (Post Office Protocol), which is used by a MUA (Message User Agent) to retrieve email messages stored by a MDA (Message Delivery Agent). See the diagram "Email Processing and Software Agents / Protocols" listed in the last section.
The original version of POP was published in 1984 by Joyce K. Reynolds in "RFC918 - Post Office Protocol" ( datatracker.ietf.org/doc/html/rfc918).
The 3rd version of POP was published in 1984 by J. Reynolds and M. Rose in "RFC1939 - Post Office Protocol - Version 3" ( datatracker.ietf.org/doc/html/rfc1939).
Here is a sample session of retrieving an email message with POP3 using "telnet" as the MUA. A Dovecot server is used to access email messages stored by a MDA.
herong$ telnet 127.0.0.1 110
Trying 127.0.0.1
Connected to 127.0.0.1.
Escape character is '^]'.
+OK Dovecot ready.
USER herong
+OK
PASS TopSecret
+OK Logged in.
STAT
+OK 2 708
LIST
+OK 2 messages:
1 416
2 292
.
RETR 1
+OK 416 octets
Return-Path: <herong@herongyang.com>
X-Original-To: herong
Delivered-To: herong@herongyang.com
Received: from localhost (localhost [IPv6:::1])
by mail.herongyang.com (Postfix) with ESMTP id 5EABD266002B
for <herong>; 15 Nov 2023 06:19:34 -0500 (EST)
Message-Id: <20231113111946.5EABD266002B@mail.herongyang.com>
Date: 15 Nov 2023 06:19:34 -0500 (EST)
From: herong@herongyang.com
Hello world!
.
QUIT
+OK Logging out.
Connection closed by foreign host.
Note that retrieving email messages with POP3 is not secure, because data is transmitted in clear text. So most of email systems are not using POP3 directly anymore. They are using the POP3S (Post Office Protocol 3 Secure) method to secure the POP3 communication. This is done by wrapping the POP3 communication under a SSL (Secure Socket Layer) or TLS (Transport Layer Security) connection. See next section for more details on POP3S.
Table of Contents
Postfix - Mail Transport Agent (MTA)
SSL/TLS Secure Connections with Postfix Server
Dovecot - IMAP and POP3 Server
SSL/TLS Secure Connections with Dovecot Server
Email Client Tools - Mail User Agents (MUA)