In computing Computing, also known as computer science, is usually defined as the activity of using and improving computer technology, computer hardware and software. It is the computer-specific part of information technology. Computer science is the study and the science of the theoretical foundations of information and computation and their implementation, the Post Office Protocol (POP) is an application-layer Application Layer is a term used in categorizing protocols and methods in architectural models of computer networking. Both the OSI model and the Internet Protocol Suite define application layers Internet standard In computer network engineering, an Internet Standard is a normative specification of a technology or methodology applicable to the Internet. Internet Standards are created and published by the Internet Engineering Task Force (IETF) protocol In computing and telecommunications, a protocol or communications protocol is a formal description of message formats and the rules for exchanging those messages. Protocols may include signaling, authentication and error detection and correction capabilities. In its simplest form, a protocol can be defined as the rules governing the syntax, used by local e-mail clients An email client, email reader, or more formally mail user agent , is a computer program that runs on a user's computer used to manage the user's email. Popular email clients include Microsoft Outlook, Pegasus Mail, Mozilla's Thunderbird, or Apple Inc.'s Mail to retrieve e-mail Electronic mail, commonly called email or e-mail, is a method of exchanging digital messages across the Internet or other computer networks. Email systems are based on a store-and-forward model in which email server computer systems accept, forward, deliver and store messages on behalf of users, who only need to connect to the email infrastructure, from a remote server Within Internet message handling services , a message transfer agent or mail transfer agent (MTA) or mail relay is a computer process or software agent that transfers electronic mail messages from one computer to another, in single hop application-level transactions. A MTA implements both the client (sending) and server (receiving) portions of the over a TCP/IP The Internet Protocol Suite is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard. Today's IP networking connection. POP and IMAP The Internet Message Access Protocol is one of the two most prevalent Internet standard protocols for e-mail retrieval, the other being the Post Office Protocol (POP). Virtually all modern e-mail clients and mail servers support both protocols as a means of transferring e-mail messages from a server (Internet Message Access Protocol) are the two most prevalent Internet standard protocols for e-mail retrieval. Virtually all modern e-mail clients and servers support both. The POP protocol has been developed through several versions, with version 3 (POP3) being the current standard.
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Overview
POP supports simple download-and-delete requirements for access to remote mailboxes (termed maildrop in the POP RFC's). Although most POP clients have an option to leave mail on server after download, e-mail clients using POP generally connect, retrieve all messages, store them on the user's PC as new messages, delete them from the server, and then disconnect. Other protocols, notably IMAP, (Internet Message Access Protocol The Internet Message Access Protocol is one of the two most prevalent Internet standard protocols for e-mail retrieval, the other being the Post Office Protocol (POP). Virtually all modern e-mail clients and mail servers support both protocols as a means of transferring e-mail messages from a server) provide more complete and complex remote access to typical mailbox operations. Many e-mail clients support POP as well as IMAP to retrieve messages; however, fewer Internet Service Providers An Internet service provider , also sometimes referred to as an Internet access provider (IAP), is a company that offers its customers access to the Internet[citation needed]. The ISP connects to its customers using a data transmission technology appropriate for delivering Internet Protocol Paradigm, such as dial-up, DSL, cable modem, wireless or (ISPs) support IMAP.
A POP3 server listens on well-known port In computer networking, the protocols of the Transport Layer of the Internet Protocol Suite, most notably the Transmission Control Protocol and the User Datagram Protocol (UDP), but also other protocols, use a numerical identifier for the data structures of the endpoints for host-to-host communications. Such an endpoint is known as a port and the 110. Encrypted communication for POP3 is either requested after protocol initiation, using the STLS command, if supported, or by POP3S, which connects to the server using Transport Layer Security Transport Layer Security and its predecessor, Secure Socket Layer (SSL), are cryptographic protocols that provide security for communications over networks such as the Internet. TLS and SSL encrypt the segments of network connections at the Transport Layer end-to-end (TLS) or Secure Sockets Layer (SSL) on well-known TCP port 995 (e.g. Google Gmail).
Available messages to the client are fixed when a POP session opens the maildrop, and are identified by message-number local to that session or, optionally, by a unique identifier assigned to the message by the POP server. This unique identifier is permanent and unique to the maildrop and allows a client to access the same message in different POP sessions. Mail is retrieved and marked for deletion by message-number. When the client exits the session, the mail marked for deletion is removed from the maildrop.
History
POP (POP1) is specified in RFC 918, POP2 by RFC 937. The original specification of POP3 is RFC 1081. Its current specification is RFC 1939, updated with an extension mechanism, RFC 2449 and an authentication mechanism in RFC 1734.
The original POP3 specification supported only an unencrypted In cryptography, encryption is the process of transforming information using an algorithm (called cipher) to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information (in cryptography, referred to as ciphertext). In many contexts, the word encryption USER/PASS login mechanism or Berkeley .rhosts rlogin is a software utility for Unix-like computer operating systems that allows users to log in on another host via a network, communicating via TCP port 513 access control. POP3 currently supports several authentication Authentication is the act of establishing or confirming something (or someone) as authentic, that is, that claims made by or about the subject are true ("authentification" is a French language variant of this word). This might involve confirming the identity of a person, tracing the origins of an artifact, ensuring that a product is what methods to provide varying levels of protection against illegitimate access to a user's e-mail. Most are provided by the POP3 extension mechanisms. POP3 clients support SASL authentication methods via the AUTH extension. MIT Project Athena also produced a Kerberized version.
RFC 1460 introduced APOP into the core protocol. APOP is a challenge/response protocol which uses the MD5 In cryptography, MD5 is a widely used cryptographic hash function with a 128-bit hash value. Specified in RFC 1321, MD5 has been employed in a wide variety of security applications, and is also commonly used to check the integrity of files. However, it has been shown that MD5 is not collision resistant; as such, MD5 is not suitable for hash function A cryptographic hash function is a deterministic procedure that takes an arbitrary block of data and returns a fixed-size bit string, the hash value, such that an accidental or intentional change to the data will change the hash value. The data to be encoded is often called the "message", and the hash value is sometimes called the in an attempt to avoid replay attacks and disclosure of the shared secret In cryptography, a shared secret is a piece of data only known to the parties involved in a secure communication. The shared secret can be a password, a passphrase, a big number or an array of randomly chosen bytes. Clients implementing APOP include Mozilla Thunderbird Mozilla Thunderbird is a free, open source, cross-platform e-mail and news client developed by the Mozilla Foundation. The project strategy is modeled after Mozilla Firefox, a project aimed at creating a web browser. On December 7, 2004, version 1.0 was released, and received over 500,000 downloads in its first three days of release, and 1,000,000, Opera Opera is a web browser and Internet suite developed by Opera Software. The browser handles common Internet-related tasks such as displaying web sites, sending and receiving e-mail messages, managing contacts, chatting on IRC, downloading files via BitTorrent, and reading Web feeds. Opera is offered free of charge for personal computers and mobile, Eudora Eudora is an e-mail client used on the Apple Macintosh and Microsoft Windows operating systems. It also supports several palmtop computing platforms, including Newton and the Palm OS. The software was named after American author Eudora Welty, because of her short story Why I Live at the P.O. Eudora was developed in 1988 by Steve Dorner, who worked, KMail Kontact is a personal information manager and groupware software suite for KDE. It supports calendars, contacts, notes, to-do lists, news, and email. It uses KParts to embed the various applications into the container application, Novell Evolution Evolution or Novell Evolution is the official personal information manager and workgroup information management tool for GNOME. It combines e-mail, calendar, address book, and task list management functions. It has been an official part of GNOME since version 2.8 in September 2004. Evolution development is sponsored primarily by Novell, RimArts' Becky! Becky! is an e-mail client developed by the Japanese company RimArts from Matsudo City, Chiba. In the early 2000s, it had received attention in East Asia due to good support for CJKV characters. It supports multiple accounts using the standard POP3/SMTP or IMAP protocols, with or without SSL, including the APOP security feature, and supports PGP,[1] Windows Live Mail Windows Live Mail is an e-mail client from Microsoft's Windows Live set of products. It is intended to be a successor for Outlook Express on Windows XP and Windows Mail on Windows Vista. The Windows Live Mail version numbering starts at 12 because this application is an advancement of Outlook Express/Windows Mail, not an entirely new application, PowerMail, and Mutt Mutt is a text-based e-mail client for Unix-like systems. It was originally written by Michael Elkins in 1995 and released under the GNU General Public License version 2 or any later version.
An informal proposal has been outlined for a POP4 specification, complete with a working server implementation. The proposed POP4 extension adds basic folder management, multipart message support, as well as message flag management, allowing for a light protocol which supports some popular IMAP features which POP3 currently lacks. However, in doing so, it shares with IMAP the embedding in a communication protocol a specific model of a mailbox, which, although common, is not universal.
No progress has been observed in the POP4 specification since 2003.
Extensions
An extension mechanism was proposed in RFC 2449 to accommodate general extensions as well as announce in an organized manner support for optional commands, such as TOP and UIDL. The RFC did not intend to encourage extensions, and reaffirmed that the role of POP3 is to provide simple support for mainly download-and-delete requirements of mailbox handling.
The extensions are termed capabilities and are listed by the CAPA command. Except for APOP, the optional commands were included in the initial set of capabilities. Following the lead of ESMTP (RFC 2821), capabilities beginning with an X signify local capabilities.
STLS
POP uses the Transmission Control Protocol The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite (the other being Internet Protocol, or IP), so the entire suite is commonly referred to as TCP/IP. Whereas IP handles lower-level transmissions from computer to computer as a message makes its way on port number In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint used by Transport Layer protocols of the Internet Protocol Suite, such as Transmission Control Protocol and User Datagram Protocol (UDP). A specific port is identified by its number, commonly known as the port 110. Transmission may be encrypted using Transport Layer Security Transport Layer Security and its predecessor, Secure Socket Layer (SSL), are cryptographic protocols that provide security for communications over networks such as the Internet. TLS and SSL encrypt the segments of network connections at the Transport Layer end-to-end (TLS) or Secure Sockets Layer Transport Layer Security and its predecessor, Secure Socket Layer (SSL), are cryptographic protocols that provide security for communications over networks such as the Internet. TLS and SSL encrypt the segments of network connections at the Transport Layer end-to-end (SSL). This is negotiated in the POP3 protocol using the STLS command. Some clients and servers, such as Google Gmail, instead use the deprecated alternate-port method, which uses TCP port 995 (POP3S).
XTND XMIT
Irrespective of the mail retrieval protocol, e-mail clients typically use the Message Submission flavor of the Simple Mail Transfer Protocol Simple Mail Transfer Protocol is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. SMTP was first defined in RFC 821 (STD 15) (1982), and last updated by RFC 5321 (2008) which includes the extended SMTP (ESMTP) additions, and is the protocol in widespread use today. SMTP is specified for (SMTP) to send messages. POP3 contains a protocol extension, known as "XTND XMIT", that allows clients to transmit outbound mail. The Qualcomm Qualcomm is a wireless telecommunications research and development company, as well as the largest fabless chip supplier in the world, based in San Diego, California 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.
See XTND Extensions.
SDPS
Demon Internet Demon Internet is a British Internet Service Provider. It was one of the earliest ISPs, one of the UK's first, especially targeting the "dialup" audience. It started on on 1 June 1992 from an idea posted on CIX by Cliff Stanford of Demon Systems Ltd. The branch in the Netherlands started in 1996, and was sold to KPN in June 2006. The introduced extensions to POP3 that allow multiple accounts per domain, and has become known as Standard Dial-up POP3 Service (SDPS).[1] To access each account, the username includes the hostname, as john@hostname or john+hostname.
Google Apps uses the same method.
Comparison with IMAP
Clients which leave mail on server generally use the UIDL command get the current association of message-numbers to message identified by its unique identifier. The unique identifier is arbitrary, and might be repeated if the mailbox contains identical messages. In contrast, IMAP uses a 32-bit unique identifier (UID) that is assigned to messages in ascending (although not necessarily consecutive) order as they are received. When retrieving new messages, an IMAP client requests the UIDs greater than the highest UID among all previously-retrieved messages, whereas a POP client must fetch the entire UIDL map. For large mailboxes, this can require significant processing.
MIME MIME's use, however, has grown beyond describing the content of e-mail to describing content type in general, including for the web serves as the standard for attachments and non-ASCII The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text. Most modern character-encoding schemes are based on ASCII, though they support many more characters than did 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.
Dialog example
RFC 1939 APOP support indicated by <1896.697170952@dbc.mtview.ca.us> here:
S: <wait for connection on TCP port 110> C: <open connection> 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: <the POP3 server sends message 1> S: . C: DELE 1 S: +OK message 1 deleted C: RETR 2 S: +OK 200 octets S: <the POP3 server sends message 2> C: QUIT S: +OK dewey POP3 server signing off (maildrop empty) C: <close connection> S: <wait for next connection>
POP3 servers without the optional APOP command expect the client to log in with the USER and PASS commands:
C: USER mrose S: +OK User accepted C: PASS mrosepass S: +OK Pass accepted
Server implementations
- Apache James Apache James, aka Java Apache Mail Enterprise Server or some variation thereof, is an open source SMTP and POP3 mail transfer agent and NNTP news server written entirely in Java. James is maintained by contributors to the Apache Software Foundation, with initial contributions by Serge Knystautas
- Citadel/UX Citadel/UX is a collaboration suite (messaging and groupware) that is descended from the Citadel family of programs which became popular in the 1980s and 1990s as a bulletin board system platform. It is designed to run on open source operating systems such as Linux or BSD. Although it is still being used widely[citation needed] on bulletin board
- Courier Mail Server The Courier mail server is a mail transfer agent server that provides ESMTP, IMAP, POP3, SMAP, webmail, and mailing list services with individual components. It is best known for its IMAP server component
- Cyrus IMAP server
- Dovecot
- Eudora Internet Mail Server
- Nginx nginx is a lightweight, high performance web server/reverse proxy and e-mail (IMAP/POP3) proxy, licensed under a BSD-like license. It runs on UNIX, GNU/Linux, BSD variants, Mac OS X, Solaris, and Microsoft Windows
- qmail-pop3d qmail is a mail transfer agent that runs on Unix. It was written, starting December 1995, by Daniel J. Bernstein as a more secure replacement for the popular Sendmail program. qmail's source code is in the public domain, making qmail free software
- Qpopper
- RePOP
- UW IMAP
- Zimbra Zimbra Collaboration Suite is a groupware product created by Zimbra, Inc., located in San Mateo, California, USA. The company was purchased by Yahoo! in September 2007, and subsequently purchased by VMware on Tuesday, January 12, 2010. The software consists of both client and server components. Two versions of Zimbra are available: an open-source
Related Requests For Comments (RFCs)
- RFC 918 - POST OFFICE PROTOCOL
- RFC 937 - POST OFFICE PROTOCOL - VERSION 2
- RFC 1081 - Post Office Protocol - Version 3
- RFC 1939 – Post Office Protocol - Version 3 (STD 53)
- RFC 1957 – Some Observations on Implementations of the Post Office Protocol (POP3)
- RFC 2195 – IMAP/POP AUTHorize Extension for Simple Challenge/Response
- RFC 2384 – POP URL Scheme
- RFC 2449 – POP3 Extension Mechanism
- RFC 2595 – Using TLS with IMAP, POP3 and ACAP
- RFC 3206 – The SYS and AUTH POP Response Codes
- RFC 5034 – The Post Office Protocol (POP3) Simple Authentication and Security Layer (SASL) Authentication Mechanism
See also
- Internet Message Access Protocol The Internet Message Access Protocol is one of the two most prevalent Internet standard protocols for e-mail retrieval, the other being the Post Office Protocol (POP). Virtually all modern e-mail clients and mail servers support both protocols as a means of transferring e-mail messages from a server (IMAP)
- Simple Mail Transfer Protocol Simple Mail Transfer Protocol is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. SMTP was first defined in RFC 821 (STD 15) (1982), and last updated by RFC 5321 (2008) which includes the extended SMTP (ESMTP) additions, and is the protocol in widespread use today. SMTP is specified for (SMTP)
- E-mail client An email client, email reader, or more formally mail user agent , is a computer program that runs on a user's computer used to manage the user's email. Popular email clients include Microsoft Outlook, Pegasus Mail, Mozilla's Thunderbird, or Apple Inc.'s Mail
- webmail Webmail is an email service intended to be primarily accessed via a web browser, as opposed to through a desktop email client. Some webmail providers use dedicated websites to providing email services, including Gmail, Yahoo! Mail, Hotmail, and AOL Mail; but there are many internet service providers which provide webmail services as part of their
- POP3 clients: getmail getmail is a simple mail retrieval agent intended as a replacement for fetchmail, implemented in Python. It can retrieve mail from POP3, IMAP4 and Standard Dial-up POP3 Service servers, with or without SSL. It supports simple and domain mailboxes, mail filtering via any arbitrary program, and supports a wide variety of mail destination types,, fetchmail Fetchmail is an open-source software utility for POSIX-compliant operating systems which is used to retrieve e-mail from a remote POP3, IMAP, ETRN or ODMR mail server to the user's local system. It was developed from the popclient program, written by Carl Harris
- email encryption
References
- ^ (Japanese), (Becky! tutorial), 2001/04/26
Further reading
- Hughes, L (1998). Internet e-mail Protocols, Standards and Implementation. Artech House Publishers. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0890069395.
- Johnson, K (2000). Internet Email Protocols: A Developer's Guide. Addison-Wesley Professional. ISBN 0201432889.
- Loshin, P (1999). Essential Email Standards: RFCs and Protocols Made Practical. John Wiley & Sons. ISBN 0471345970.
- Rhoton, J (1999). Programmer's Guide to Internet Mail: SMTP, POP, IMAP, and LDAP. Elsevier. ISBN 1555582125.
- Wood, D (1999). Programming Internet Mail. O'Reilly. ISBN 1565924797.
External links
Categories: Internet mail protocols
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Q. Scenario: You were hired as network designer/engineer in a prominent company somewhere in US. One day your boss submit a project implementation in your office, this project is the data centralization of all departments/division in the company. After 5 months you finished the project, upon the implementation; the users got troubled because of the network being implemented and here are the problems.. 1. Problem of Internet Protocol (IP) Address Duplication (Data transmission always collide each other and server produce unrealistic report, thousands of account did not post in the server) 2. Connectivity Problem. (The company invested 5 million dollars to buy your requested network materials a high-end Ethernet media but the data… [cont.]
Asked by RAJ - Thu Nov 22 07:54:02 2007 - - 6 Answers - 0 Comments
A. Let me understand, you want another professional IT/IS person to do your job for you, a job that you are suppose to be able to do because YOU were hired for it. Do your job, after all you are suppose to be able to do it, or did you lie and exaggerate your specific qualifications to acquire the job. I would not make if far in my job if i could not do it, nor would i expect to. I do this for a living, and i find myself cleaning up other peoples messes, and fixing stuff that they were suppose to be able to do. Oh they are good at buying equipment, and spending other peoples money. Also having other people do their job, as long as other people don't get the monies or credit.
Answered by mhp_wizo_93_418 - Thu Nov 22 08:00:08 2007
