2.4. Protocol POP3

2.4.1. Connection

If port is not specified, the standard POP3 port (110)
If port is not specified, 995, the standard POP3-over-SSL port is used

2.4.2. `poplib` API

Table 2.12. `poplib` API
Method	Arguments	Description
`poplib.POP3()`	`host`, `port=POP3_PORT`, `timeout=None`	This class implements the actual POP3 protocol
`poplib.POP3_SSL()`	`host`, `port=POP3_SSL_PORT`, `keyfile=None`, `certfile=None`, `timeout=None`, `context=None`	This is a subclass of POP3 that connects to the server over an SSL encrypted socket
`POP3.user()`	`username`	Send user command, response should indicate that a password is required
`POP3.pass_()`	`password`	Send password, response includes message count and mailbox size
`POP3.apop()`	`user`, `secret`	Use the more secure APOP authentication to log into the POP3 server
`POP3.stat()`		Get mailbox status. The result is a tuple of 2 integers: (message count, mailbox size)
`POP3.list()`	`which=None`	Request message list, result is in the form `(response, ['mesg_num octets', ...], octets)`
`POP3.retr()`	`which`	Retrieve whole message number which, and set its seen flag. Result is in form `(response, ['line', ...], octets)`
`POP3.dele()`	`which`	Flag message number which for deletion
`POP3.rset()`		Remove any deletion marks for the mailbox
`POP3.quit()`		Signoff: commit changes, unlock mailbox, drop connection
`POP3.top()`	`which`, `howmuch`	Retrieves the message header plus howmuch lines of the message after the header of message number which
`POP3.utf8()`		Try to switch to UTF-8 mode. Returns the server response if successful, raises error_proto if not
`POP3.stls()`	`context=None`	Start a TLS session on the active connection as specified in RFC 2595. This is only allowed before user authentication

2.4.3. Retrieve Messages with POP3

Code 2.10. Secured connection to the SMTP server

import poplib


POP3_HOST = 'localhost'
POP3_PORT = 995
POP3_USER = 'myusername'
POP3_PASS = 'mypassword'


server = poplib.POP3_SSL(host=POP3_HOST, port=POP3_PORT, timeout=30)
server.user(POP3_USER)
server.pass_(POP3_PASS)

status, messages, length = server.list()

for message in messages:
    msgid, length = message.split()
    status, content, length = server.retr(int(msgid))
    mail = '\r\n'.join(line.decode() for line in content)

    print(mail)
    print('-' * 30)

"""
Return-Path: <root@ip-172-31-5-83.eu-central-1.compute.internal>
X-Original-To: upload@localhost
Delivered-To: upload@localhost
Received: by ip-172-31-5-83.eu-central-1.compute.internal (Postfix, from userid 0)
	id 2481544BD5; Thu, 23 May 2019 07:36:17 +0000 (UTC)
Subject: test
To: <upload@localhost>
X-Mailer: mail (GNU Mailutils 3.4)
Message-Id: <20190523073617.2481544BD5@ip-172-31-5-83.eu-central-1.compute.internal>
Date: Thu, 23 May 2019 07:36:17 +0000 (UTC)
From: root <root@ip-172-31-5-83.eu-central-1.compute.internal>

hello
------------------------------
"""