SMTPBeamer on my Windows 2003 Web server
This is an easy-to-set-up e-mail server. Enable advanced features as you go. I started out downloading the catchall POP3 mail from my first hosted domain years ago with SMTPBeamer. Today, I use SMTPBeamer on my Windows 2003 Web server. It handles the mail for all my domains and the domains I host. You can setup SMTPBeamer yourself. Just follow the instructions on the bottom of this page.
Peter Banz
SMTP is only useful as a transport protocol between mail servers. It does not deliver mail to a user’s mailbox, nor allow remote users to retrieve mail from the server. Local delivery is a function of the mail system in use. For example, cc:Mail uses a disk-based postoffice to store mail for each individual user on that system. An SMTP server for cc:Mail would accept messages on behalf of the cc:Mail users, but would not necessarily deliver that mail to the user. The cc:Mail postoffice server would likely handle the local delivery independently of the SMTP gateway.
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Setting Up POP3 and SMTP E-Mail Accounts in Outlook XPby David Horowitz |
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| Perhaps you’d like to learn a little more about setting up POP3/SMTP access from Outlook. Well, you’re in luck – keep reading! POP3 - The Technical StuffPOP3 stands for Post Office Protocol - Version 3. The “governing body” that specifies how POP3 works is the Internet Engineering Task Force (IETF). The IETF main web site is www.ietf.org. You can find detailed information about POP3 on the IETF RFC Editor web site – www.rfc-editor.org. Specifically, the POP3 specification document can be found at ftp://ftp.rfc-editor.org/in-notes/rfc1939.txt. read more... |
I was asked some time ago to develop software which involved extracting bodies and subject lines from emails. "Humm ...", I thought, "connect to mail server on 110, send POP3 commands, receive data, sorted!". Indeed, at my first attempt it was a piece of cake: reading emails - no problem. Colleagues working at my company were evangelizing about what we could do: "Yeah mate, we can automatically process emails, no sweat".
This is a full-transparent proxy-server for email clients. It runs on a Linux box with iptables (for port re-direction)[1]. It can be used to provide email scanning from the internet, to any internal network and is ideal for helping to protect your "Other OS" LAN from harm, especially when used in conjunction with a firewall and other Internet Proxy servers.
It is designed to enable scanning of incoming/outgoing email messages for Virus's, Worms, Trojans, Spam (read as "Un-solicited Bulk Email"), and harmfull attachments. Because viewing HTML mail can enable a "Spammer" to validate an email address (via Web bugs), it can also provide HTML stripping.
This project is maintained by Jack S. Lai
P3Scan is a derived work of POP3VScan as written by Folke Ashberg
It's intent is to provide a follow on program to POP3-Virusscan-Proxy 0.4
It is based upon his program but provides numerous changes to include scanning email for spam, hardening the program, addaption to today's email environment, and many, many other changes.
read more...The MarshallSoft SMTP/POP3 Email component Library for Delphi (SEE4D) is a library of functions providing easy control of the SMTP (Simple Mail Transport Protocol) and POP3 (Post Office 3) protocols.
The SMTP/POP3 Email development toolkit provides a simple interface to send and receive email, including multiple MIME base64 and quoted-printable encoded attachments from within a Borland Delphi application. Knowledge of Winsock and TCP/IP is not needed.
SEE4D provides the functionality to easily and quickly develop software applications that can send, receive and parse mail.
Secure IMAP (and POP3)v 2.6 Roberto Cecchini
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Contents |  Introduction OpenSSL Installation Certificate Request and Installation stunnel Installation stunnel on the Server E-mail Clients (Unix) Configuration E-mail Clients (Windows) Configurationread more... |
These free services give you a free email address with either a POP3 mailbox access, IMAP access, web email access, or email aliases that will forward or redirect email sent to that address to another. They may be used by people who are looking for an email address that is independent of their ISP, and thus hopefully more permanent that that given by the ISP.
MORE INFORMATIONLog Example - Failed Login
POP3 is a protocol for retrieving mail from a mailbox on a remote server. It is a simple protocol that does not provide any advanced mail or folder management capabilities - these are offered by IMAP, and an IMAP component is a part of Rebex Mail for .NET as well.
popa3d is a tiny POP3 daemon designed with security as the primary goal. You can read more about its design, check out the change log, or download a popa3d tarball (the latest stable version is recommended) and refer to the documentation inside.
Answer:
POP (Post Office Protocol) is used to provide simple remote access to mailboxes. POP3 is the latest version of POP. With POP3, once mail clients connect and download their messages, the messages are typically removed from the server and stored on the client's local machine.
This means that you have to ensure that the all the machines are backed up in order to prevent you loosing any information in email messages. To resolve this problem, you could use the IMAP4 or Web Mail clients which allow messages to be manipulated on the server.
Answer:
POP (Post Office Protocol) is used to provide simple remote access to mailboxes. POP3 is the latest version of POP. With POP3, once mail clients connect and download their messages, the messages are typically removed from the server and stored on the client's local machine.
IMAP (Internet Message Access Protocol) is richer in functionality than POP and is designed to allow clients to access and manage mailboxes on the server as if they were local. IMAP is a much more complex protocol than POP, with less client support.
checkpw-pop3 is a checkpassword compatible program that authenticates against a POP3 server.
It is useful when one needs to use SMTP AUTH with an SMTP server that cannot directly access the POP3 server or user account database.
This software is public domain.
POP stands for Post Office Protocol. It is a method of accessing electronic mail that is kept on a dedicated mail server. POP3 permits an email "client" program (MUA) to download remote messages to the client computer. POP was designed for "offline" message access and works best when one uses a single computer, wherein messages are downloaded and then deleted from the mail server. This mode of access is not compatible with access from multiple computers since it tends to sprinkle messages across all of the computers used for mail access. Thus, unless all of those machines share a common file system, the offline mode of access that POP was designed to support effectively ties the user to one computer for message storage and manipulation.
The protocol includes operations for: checking for new messages; permanently removing messages; setting and clearing flags.
Qpopper
The most widely-used POP3 server for UNIX, Linux, etc.
Qpopper 4.0.8 is now available.
Still using version 2.53 ? Read up on the benefits of 3.0 and 3.1 before you move to 4.0.
Qpopper 4.0.8 Features:
This is the second in a series of articles on Internet programming with Microsoft's new C# programming language. In the first article, I wrote a simple SMTP class. In this article, I'm going to write a simple POP3 class. The SMTP class that I wrote was not very useful, except maybe as an exercise, as there already exists a similar SMTP class in the Web.Mail namespace of the .NET framework called SmtpMail. Our POP3 class in this article will be a little more useful as it doesn't already exist in the .NET framework. I have encountered many POP3 C# classes in my searches of the Internet and most were sufficient to begin programming email clients.
Christensen Software provides high quality solutions for server-based email and communications systems.
On these pages you will find information about our current products and trial versions available for download.
We are constantly working to update our products and to create new solutions for handling email and other communications. Make sure to check back often.
To German Version (of this Website and german language versions of our software)
The new version of this popular software product — Native POP3 Connector (hereafter NPC) — is an extension for Microsoft® Exchange Server 2000/2003 and Microsoft® Small Business Server 2000/2003. It is a connector or a gateway to use the terms of the aforementioned products. In this version a lot of program features have been added and all known issues from previous versions have been fixed.
NPC offers a standard solution for the problem with receiving mail through the POP3 protocol for Microsoft Exchange Server 2000/2003 and Microsoft Small Business Server 2000/2003 with Microsoft Exchange Server installed (SBS 2000/2003). NPC is a solution with an affinity to Microsoft Exchange Server 2000/2003 and SBS 2000/2003 — Connector. During the installation, the administrator has an opportunity to install a new type into the Connectors Exchange System Manager group (also available in SBS Administration Console): Native POP3 Connector. Upon installation, all administration procedures are performed in a way standard for Microsoft Exchange 2000/2003 and SBS 2000/2003 — by editing the properties of the Connector installed via Exchange System Manager.
POP3 Extension Mechanism
See:
Description
| Class Summary | |
|---|---|
| POP3Folder | A POP3 Folder (can only be "INBOX"). |
| POP3Message | A POP3 Message. |
| POP3SSLStore | A POP3 Message Store using SSL. |
| POP3Store | A POP3 Message Store. |
In this section
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The POP3 service supplements existing functionality in Windows Server 2003 provided by the SMTP service, which receives e-mail messages. The POP3 service makes e-mail messages available for download from a server, enabling a server to host e-mail accounts and provide basic e-mail access.
With only some simple scripts your applications will be enabled to retrieve emails based on POP3 & IMAP4 protocol and parse emails based on MIME with this powerful pop3/imap4 component.
Important notice:* For C#, Visual Basic.NET, Managed C++, J#, JScript.NET and ASP.NET developers, we strongly recommend that you use the pure .NET class EAGetMail POP3 & IMAP4 Component instead of ANPOP POP3 Component.
What is POP3?
POP3 is a client-server protocol in which email is received and held by a mail server. Messages are downloaded to a local computer all at once, thereby making offline reading easier. You can specify whether to keep copies of the messages on the server. The default port number for POP3 is 110.
What is the POP3 Service?
The POP3 (Post Office Protocol version 3) service is an email service that retrieves email messages. Administrators can use the POP3 service to store and manage email accounts on the mail server. Although the Microsoft Exchange family provides more flexibility to a mail server, the user experience on an email client (such as Outlook Express) - when sending or receiving email - is the same. The end user will not notice the difference when downloading their personal email from the server.
Pros
Cons
Below is an explanation of the general difference between the IMAP and POP3 email protocols.
IMAP account
Using this protocol, all your mail stays on the server in multiple folders, some of which you have created. This enables you to connect to any computer and see all your mail and mail folders. In general, IMAP is great if you have a dedicated connection to the Internet or you like to check your mail from various locations.
POP3
With this type of email account you only have one folder, the Inbox folder. When you open your mailbox, new mail is moved from the host server and saved on your computer. If you want to be able to see your old mail messages, you have to go back to the computer where you last opened your mail.
With this type of account you do not have to stay logged on to the Internet. You can log on when you want to receive and send new messages. Once your new messages have been downloaded to your computer you can log off to read them. This option is good when you connect with your modem to DAS and are charged for your connection or you have an older computer.
Leave mail on server vs. Remove mail from server
If you use the POP3 protocol and you read your mail from multiple computers, you will want to "leave mail on the server." The reason for this is so that the mail in your Inbox will be available to you at all times. If you do not leave mail on the server, all the mail in your Inbox will be downloaded to the computer you are currently using. If you only read your mail from one location, then there is no need to "leave mail on the server." You will see instructions on how to set this option when you go through the steps to set up your email program.
Why choose IMAP rather than POP3 with "leave mail on server"? With POP3 "leave mail on server" only your email messages are on the server, but with IMAP your email folders are also on the server.
How many times have you had problems sending SQL MAIL or SQL Agent Mail from SQL Server because the Exchange server was taken down or not working? Have you ever tried to connect up SQL Mail and/or SQL Agent mail to Exchange through a firewall or across domains, only to find out that you cannot use your Exchange in these situations? Maybe you don't have Exchange but you would still like to setup SQL Server to send email. If you have experienced these problems then you might want to consider using POP3 and SMTP services for supporting your SQL Mail and SQL Agent mail requirements. This article will discuss how to setup SQL Server to use POP3 and SMTP services to support SQL Mail and SQL Agent mail.
Introduction
Many software systems require the ability to connect with and provide services that interact with email in different ways. Perhaps you’re writing software for a bulletin board that must notify users when new responses are posted in certain topics, or a piece of scheduling software that must notify users when new engagements are assigned to them. There are, of course, many further applications for integration between business or Web software with email.
Integrating with email allows for advantages from both business and portability perspectives. From a business perspective, integrating your software with email allows users to use their email accounts as a central place in which to get notifications and information about a wide range of business objectives. From a portability viewpoint, email adds a layer of abstraction, making it possible for a user to receive alerts from your software in any way they choose: via a classic email client, a Web client from a public computer or home, or even a cell phone or Blackberry capable of accessing standard email protocols.
This article series will discuss how to use the email libraries built in to Python. I will describe how to access email on both POP and IMAP servers, how to parse this mail into easily usable data structures, and how to create email items and then send them through an SMTP server.
The Post Office Protocol (Pop3) allows computers to retrieve messages from mailboxes on mail servers. This can be done via email clients or via webbased pop3 readers. Since The POP3 protocol does not support multi-mailbox accounts, it is a better choice to find an imap service. IMAP (Internet Messaging Access Protocol) is more sophisticated than the Post Office Protocol (POP3) protocol. Messages can be archived in folders, mailboxes can be shared, and a user can access multiple mail servers. There is also better integration with MIME, which is used to attach files. On this page you will get the list af free pop3, free imap and free smtp service providers available worldwide! Meanwhile SMTP (Simple Mail Transfer Protocol) servers route SMTP messages throughout the Internet to a mail server, such as POP3 or IMAP4, which provides a message store for incoming mail. You can find more info about these services and terms on F.A.Q page and through the forum. While you are browsing through the pages, please do not hesitate to contact me for any reason you have. To have up-to-date listing please inform me broken/dead links and new services you come across on the net :)
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If you have no choice but to use that kind of POP3 configuration, you may be interested in PopGrabber, a third-party POP3 connector tool.
Nothing needs to be installed on Exchange Server itself for PopGrabber to work, because it's a standalone program, not an Exchange Server add-on. When installed, it talks to an outside POP3 mailbox at regular intervals, downloads all the email there, and forwards it to another server via SMTP.
The port numbers for all actions can be user-defined, and APOP authentication is supported if you need it (although SMTP authentication is not).
Note that the target server doesn't have to be an Exchange server --any SMTP server will do-- but it works with Exchange Server as transparently as anything else.
The basic, free version of PopGrabber can talk to up to three external email accounts, and forward them all to a single SMTP server. The standard, commercial version of PopGrabber costs U.S. $35 and can retrieve email from and send email to an unlimited number of POP3 and SMTP accounts.
Both versions have a few drawbacks, though. For one, they don't support SSL, for one. However, the program's authors have a workaround for the SSL problem that involves using ClamMail, a free mail proxy and antivirus scanner.
About the author: Serdar Yegulalp is editor of Windows Insight, a newsletter devoted to hints, tips, tricks, news and goodies for all flavors of Windows users.
Another good software to use is SmartPOP2Exchange from Jam Software.
—Nick T.
Related information from SearchExchange.com:
POP
(1) Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server. Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).
There are two versions of POP. The first, called POP2, became a standard in the mid-80's and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.
(2) Short for point of presence, an access point to the Internet. ISPs have typically multiple POPs. A point of presence is a physical location, either part of the facilities of a telecommunications provider that the ISP rents or a separate location from the telecommunications provider, that houses servers, routers, ATM switches and digital/analog call aggregators.
(3) Short for Programmed Operator (POP), a pseudo-opcode in a virtual machine language executed by an interpretive program. The Programmed Operator instructions provide the ability to define an instruction set for efficient encoding by calling subprograms into primary memory.
(4) Short for picture-outside-picture POP is a feature found on some televisions that allows the user to divide the screen into two same-size pictures, enabling you to view a second program. Compare with picture-in-picture (PIP).
POP3 |
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- POP3 (Post Office Protocol 3) is the most recent version of a standard protocol for receiving e-mail. POP3 is a client/server protocol in which e-mail is received and held for you by your Internet server. Periodically, you (or your client e-mail receiver) check your mail-box on the server and download any mail, probably using POP3. This standard protocol is built into most popular e-mail products, such as Eudora and Outlook Express. It's also built into the Netscape and Microsoft Internet Explorer browsers. POP3 is designed to delete mail on the server as soon as the user has downloaded it. However, some implementations allow users or an administrator to specify that mail be saved for some period of time. POP can be thought of as a "store-and-forward" service.
An alternative protocol is Internet Message Access Protocol (IMAP). IMAP provides the user more capabilities for retaining e-mail on the server and for organizing it in folders on the server. IMAP can be thought of as a remote file server.
POP and IMAP deal with the receiving of e-mail and are not to be confused with the Simple Mail Transfer Protocol (SMTP), a protocol for transferring e-mail across the Internet. You send e-mail with SMTP and a mail handler receives it on your recipient's behalf. Then the mail is read using POP or IMAP.
The conventional port number for POP3 is 110.
Using TLS with IMAP, POP3 and ACAP
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
read more...
The SYS and AUTH POP Response Codes
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This memo proposes two response codes: SYS and AUTH, which enable
clients to unambiguously determine an optimal response to an
authentication failure. In addition, a new capability (AUTH-RESP-
CODE) is defined.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in this Document . . . . . . . . . . . . . . 2
3. Background . . . . . . . . . . . . . . . . . . . . . . . . 2
4. The SYS Response Code . . . . . . . . . . . . . . . . . . . 3
5. The AUTH Response Code . . . . . . . . . . . . . . . . . . 3
6. The AUTH-RESP-CODE Capability . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . 5
10. Author's Address . . . . . . . . . . . . . . . . . . . . . . 5
11. Full Copyright Statement . . . . . . . . . . . . . . . . . 6
read more...
POP3 AUTHentication command
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.1. Introduction
This document describes the optional AUTH command, for indicating an
authentication mechanism to the server, performing an authentication
protocol exchange, and optionally negotiating a protection mechanism
for subsequent protocol interactions. The authentication and
protection mechanisms used by the POP3 AUTH command are those used by
IMAP4.
read more...
POP3 Extension Mechanism
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
IESG Note
This extension to the POP3 protocol is to be used by a server to
express policy descisions taken by the server administrator. It is
not an endorsement of implementations of further POP3 extensions
generally. It is the general view that the POP3 protocol should stay
simple, and for the simple purpose of downloading email from a mail
server. If more complicated operations are needed, the IMAP protocol
[RFC 2060] should be used. The first paragraph of section 7 should
be read very carefully.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in this Document . . . . . . . . . . . . . 3
3. General Command and Response Grammar . . . . . . . . . . . . 3
4. Parameter and Response Lengths . . . . . . . . . . . . . . 4
5. The CAPA Command . . . . . . . . . . . . . . . . . . . . . . 4
6. Initial Set of Capabilities . . . . . . . . . . . . . . . . 5
6.1. TOP capability . . . . . . . . . . . . . . . . . . . . . 6
6.2. USER capability . . . . . . . . . . . . . . . . . . . . 6
6.3. SASL capability . . . . . . . . . . . . . . . . . . . . 7
6.4. RESP-CODES capability . . . . . . . . . . . . . . . . . 8
6.5. LOGIN-DELAY capability . . . . . . . . . . . . . . . . . 8
6.6. PIPELINING capability . . . . . . . . . . . . . . . . . 9
Gellens, et. al. Standards Track [Page 1]
RFC 2449 POP3 Extension Mechanism November 1998
6.7. EXPIRE capability . . . . . . . . . . . . . . . . . . . 10
6.8. UIDL capability . . . . . . . . . . . . . . . . . . . . 13
6.9. IMPLEMENTATION capability . . . . . . . . . . . . . . . 13
7. Future Extensions to POP3 . . . . . . . . . . . . . . . . . 14
8. Extended POP3 Response Codes . . . . . . . . . . . . . . . . 14
8.1. Initial POP3 response codes . . . . . . . . . . . . . . 15
8.1.1. The LOGIN-DELAY response code . . . . . . . . . . . 15
8.1.2. The IN-USE response code . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . 17
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 17
12. References . . . . . . . . . . . . . . . . . . . . . . . . 17
13. Authors' Addresses . . . . . . . . . . . . . . . . . . . . 18
14. Full Copyright Statement . . . . . . . . . . . . . . . . . . 19
Post Office Protocol - Version 3
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Table of Contents
1. Introduction ................................................ 2
2. A Short Digression .......................................... 2
3. Basic Operation ............................................. 3
4. The AUTHORIZATION State ..................................... 4
QUIT Command ................................................ 5
5. The TRANSACTION State ....................................... 5
STAT Command ................................................ 6
LIST Command ................................................ 6
RETR Command ................................................ 8
DELE Command ................................................ 8
NOOP Command ................................................ 9
RSET Command ................................................ 9
6. The UPDATE State ............................................ 10
QUIT Command ................................................ 10
7. Optional POP3 Commands ...................................... 11
TOP Command ................................................. 11
UIDL Command ................................................ 12
USER Command ................................................ 13
PASS Command ................................................ 14
APOP Command ................................................ 15
8. Scaling and Operational Considerations ...................... 16
9. POP3 Command Summary ........................................ 18
10. Example POP3 Session ....................................... 19
11. Message Format ............................................. 19
12. References ................................................. 20
13. Security Considerations .................................... 20
14. Acknowledgements ........................................... 20
15. Authors' Addresses ......................................... 21
Appendix A. Differences from RFC 1725 .......................... 22
read more...
POP3 has made earlier versions of the protocol obsolete, POP (informally called POP1) and POP2. In contemporary usage, the less precise term POP almost always means POP3 in the context of e-mail protocols.
The design of POP3 and its procedures supports end-users with intermittent connections (such as dial-up connections), allowing these users to retrieve e-mail when connected and then to view and manipulate the retrieved messages without needing to stay connected. Although most clients have an option to leave mail on server, e-mail clients using POP3 generally connect, retrieve all messages, store them on the user's PC as new messages, delete them from the server, and then disconnect. In contrast, the newer, more capable Internet Message Access Protocol (IMAP) supports both connected and disconnected modes of operation. E-mail clients using IMAP generally leave messages on the server until the user explicitly deletes them. This and other facets of IMAP operation allow multiple clients to access the same mailbox. Most e-mail clients support either POP3 or IMAP to retrieve messages; however, fewer Internet Service Providers (ISPs) support IMAP. The fundamental difference between POP3 and IMAP4 is that POP3 offers access to a mail drop; the mail exists on the server until it is collected by the client. Even if the client leaves some or all messages on the server, the client's message store is considered authoritative. In contrast, IMAP4 offers access to the mail store; the client may store local copies of the messages, but these are considered to be a temporary cache; the server's store is authoritative.
Clients with a leave mail on server option generally use the POP3 UIDL (Unique IDentification Listing) command. Most POP3 commands identify specific messages by their ordinal number on the mail server. This creates a problem for a client intending to leave messages on the server, since these message numbers may change from one connection to the server to another. For example if a mailbox contains five messages at last connect, and a different client then deletes message #3, the next connecting user will find the last two messages' numbers decremented by one. UIDL provides a mechanism to avoid these numbering issues. The server assigns a string of characters as a permanent and unique ID for the message. When a POP3-compatible e-mail client connects to the server, it can use the UIDL command to get the current mapping from these message IDs to the ordinal message numbers. The client can then use this mapping to determine which messages it has yet to download, which saves time when downloading. IMAP has a similar mechanism, using a 32-bit UID (Unique IDentifier) that is required to be strictly ascending. The advantage of the numeric UID is with large mailboxes; a client can request just the UIDs greater than its previously stored "highest UID". In POP, the client must fetch the entire UIDL map.
Whether using POP3 or IMAP to retrieve messages, e-mail clients typically use the SMTP_Submit profile of the SMTP protocol to send messages. E-mail clients are commonly categorized as either POP or IMAP clients, but in both cases the clients also use SMTP. There are extensions to POP3 that allow some clients to transmit outbound mail via POP3 - these are known as "XTND XMIT" extensions. The Qualcomm qpopper and CommuniGate Pro servers and Eudora clients are examples of systems that optionally utilize the XTND XMIT methods of authenticated client-to-server e-mail transmission.
MIME serves as the standard for attachments and non-ASCII text in e-mail. Although neither POP3 nor SMTP require MIME-formatted e-mail, essentially all Internet e-mail comes MIME-formatted, so POP clients must also understand and use MIME. IMAP, by design, assumes MIME-formatted e-mail.
Like many other older Internet protocols, POP3 originally supported only an unencrypted login mechanism. Although plain text transmission of passwords in POP3 still commonly occurs, POP3 currently supports several authentication methods to provide varying levels of protection against illegitimate access to a user's e-mail. One such method, APOP, uses the MD5 hash function in an attempt to avoid replay attacks and disclosure of a shared secret. Clients implementing APOP include Mozilla, Thunderbird, Opera, Eudora, KMail and Novell Evolution. POP3 clients can also support SASL authentication methods via the AUTH extension.
POP3 works over a TCP/IP connection using TCP on network port 110. E-mail clients can encrypt POP3 traffic using TLS or SSL. A TLS or SSL connection is negotiated using the STLS command. Some clients and servers, like Google Gmail, instead use the deprecated alternate-port method, which uses TCP port 995.
S:
C:
S: +OK POP3 server ready <1896.697170952@dbc.mtview.ca.us>
C: APOP mrose c4c9334bac560ecc979e58001b3e22fb
S: +OK mrose's maildrop has 2 messages (320 octets)
C: STAT
S: +OK 2 320
C: LIST
S: +OK 2 messages (320 octets)
S: 1 120
S: 2 200
S: .
C: RETR 1
S: +OK 120 octets
S:
S: .
C: DELE 1
S: +OK message 1 deleted
C: RETR 2
S: +OK 200 octets
S:
S: .
C: DELE 2
S: +OK message 2 deleted
C: QUIT
S: +OK dewey POP3 server signing off (maildrop empty)
C:
S:
POP3 servers without the optional APOP command expect you to log in with the USER and PASS commands:
C: USER mrose S: +OK User accepted C: PASS mrosepass S: +OK Pass accepted
