This article is from the LAN Mail Protocols FAQ, by John Wobus email@example.com with numerous contributions by others.
(a) What are the common extensions to POP3 and which clients/servers
POP3k - Kerberos
POP3a - AFS Kerberos
POP3x - ?
POP3t - xtnd xmit facility--allows client to send mail through additional
POP commands, thus allowing server to verify/log source of mail.
POP3r - APOP
POP3s - RPOP
POP3m - ?
POP3u - with UIDL command.
(b) What DOS protocol stacks are supported?
MS-DOSm - Lan Manager
MS-DOSn - NDIS Drivers
MS-DOSl - Lan Workplace for Dos
MS-DOSs - Sun PCNFS
MS-DOSp - Packet Drivers
MS-DOSo - ODI Drivers
MS-DOSi - IPXLink
MS-DOSf - FTP Software PC/TCP
MS-DOSk - KA9Q I think
MS-WIN? - similar
MS-WINw - WinSock compliant
MS-WIN5 - Windows 95
WIN3 - Windows 3.x winsock
WIN3/95/NT - Windows 3.x Winsock, Windows 95 and Windows NT
WIN3/95 - Windows 3.x Winsock and WIndows 95
NetWare3 - NetWare 3.x
NetWare4 - NetWare 4.x
NetWare34 - NetWare 3.x and 4.x
PHP3 - written in PHP scripting language.
Perl - written in Perl scripting language.
Java - written in Java programming language.
JavaApp - written as a Java Applet.
(c) Other notes
IMAP1 - Original IMAP: I've heard that MacMS actually uses a unique
dialect of it. Definitely obselete, unsupported, discouraged.
IMAP2b - IMAP2bis: name applied to various improved versions of IMAP2.
This development effort culminated in IMAP4.
IMAP24 - IMAP2 or IMAP4
fshare - uses file sharing.
IMAPb4 - IMAP2, IMAP2bis, or IMAP4.
IMAP41 - IMAP4rev1
MAPI - Microsoft's Messaging API
HTTP - Web-based e-mail.
MAPIs - Simple MAPI.
VIM - Lotus's Vendor Independent Messaging API
CMC - XAPIA's Common Message Calls API
AOCE - Apple Open Collaborative Environment
PROP - System-specific proprietary protocol
FCP - SoftArc's proprietary client-server protocol.
Unix/X - X Windows based
Unix/XM - Motif based
Unix/XO - OpenWindows based
UnixSHA - Solaris, HPUX & AIX
PSS - PROFS Screen Scraper
sumex-aim.stanford.edu* - almost dead as of 7/13/95, to be replaced by
Metamail - a package with which MIME messages can be processed from
basically any Unix-based mail client.
POPGate (Stalker Software) - gateway to/from Stalker's CommuniGate
system: enables both use of POP3 to get software from a POP3 server
for use within a CommuniGate community, and to allow POP3 clients to
retrieve mail from a CommuniGate server.
DigUNIX - Digital Unix
Solaris - Solaris 2.x
peer - peer-to-peer mail system
gtwy - e-mail gateway of some kind: a system that moves e-mail between two
different systems/areas. Among other things, a add-on to a
proprietary mail server that made it act as a POP or IMAP server or
that made it exchange e-mail using SMTP could be called a gateway.
(d) IMAP/MAPI adaptors:
Wollongong's Pathway Access 7/12/94
firstname.lastname@example.org's Mail-IT 7/12/94
(e) IMAP/POP3 adaptors:
Included with NCD Z-mail 4.0 for Windows 9/14/95