Editing Post Office Protocol (section)

==History==
The first version of the Post Office Protocol, POP1, was specified in RFC 918 (1984) by [[Joyce K. Reynolds]]. POP2 was specified in RFC 937 (1985).

POP3 is the version in most common use. It originated with RFC 1081 (1988) but the most recent specification is RFC 1939, updated with an extension mechanism (RFC 2449) and an authentication mechanism in RFC 1734. This led to a number of POP implementations such as Pine, [[POPmail]], and other early mail clients. 

While the original POP3 specification supported only an unencrypted USER/[[password|PASS]] [[login]] mechanism or Berkeley [[Rlogin|.rhosts]] access control, today POP3 supports several [[authentication]] 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 [[Simple Authentication and Security Layer|SASL]] authentication methods via the AUTH extension. [[Massachusetts Institute of Technology|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]] [[cryptographic hash function|hash function]] in an attempt to avoid [[replay attack]]s and disclosure of the [[shared secret]]. Clients implementing APOP include [[Mozilla Thunderbird]], Opera Mail, [[Eudora (email client)|Eudora]], [[KMail]], [[Novell Evolution]], RimArts' [[Becky!]],<ref>{{in lang|ja}}, [http://journal.mycom.co.jp/special/2001/onlinenote/005.html (Becky! tutorial)] {{Webarchive|url=https://web.archive.org/web/20100131223322/http://journal.mycom.co.jp/special/2001/onlinenote/005.html |date=2010-01-31 }}, 2001-04-26.</ref> [[Windows Live Mail]], PowerMail, [[Apple Mail]], and [[Mutt (e-mail client)|Mutt]]. RFC 1460 was obsoleted by RFC 1725, which was in turn obsoleted by RFC 1939.

===POP4===
POP4 exists only as an informal proposal adding basic folder management, multipart message support, as well as message flag management to compete with IMAP; however, its development has not progressed since 2003. There are now two known POP4 server implementations. As of October 2013, the POP4.org domain and website are now hosted by simbey.com, which also runs the other POP4 [http://www.pop4.org/ server implementation.]<ref>{{cite web
|archive-url=https://web.archive.org/web/20171021231958/http://www.pop4.org/pop4/pop4spec.html
|archive-date=2017-10-21
|url=http://www.pop4.org/pop4/pop4spec.html
|title=POP4 specification although pop is used to receive mail after system is not online.
|year=2003
|access-date=2011-10-17}}</ref>