🚀 go-pugleaf

Archive-name: LANs/mail-protocols

Serving PCs and Workstations Using a Central Mail Server on an Internet
------- --- --- ------------ ----- - ------- ---- ------ -- -- --------

  (Note: this message is prepared by John Wobus of Syracuse University,
   jmwobus@mailbox.syr.edu who welcomes updates and corrections; this
   memo has not been checked very carefully and requires a lot of
   correction at this time.  The last update was made 11/2/93).

There are advantages to collecting mail destined to PCs and
workstations on a central server, to be turned over to the PC or
workstation on demand:

- Your PC or workstation may be down quite a bit and less network
  bandwidth and less of the processing resouces of the sending computer
  are used if the computer receiving your mail is ready.
- Some people use more than one PC or workstation to read mail.
- A PC or workstation may not have the resources to store all the mail
  you receive.
- It can make your e-mail address more like other users'.

The easiest way to "implement" this is to run the central mail server
like any multi-user system: let people sign on to it and use some mail
utility.  Then PC and workstation users can use "terminal sessions" to
sign on to the central mail server and read their mail.  This has the
disadvantage of making the PC and workstation users learn and use the
central mail server's procedures.

SMTP, the "internet" mail protocol used to deliver mail between
multi-user systems only supports mail transfer initiated by the
sender.  Other protocols have been devised to allow a workstation or PC
to request transfer of mail, thus able to make use of a cnetral
server.  These include the published protocols POP (probably not used
anymore), POP2, POP3, IMAP2, IMAP3 and DMSP.

POP, POP2, POP3:  These are rather minimal and are designed to be so.
The three are similar but not enough alike to be interoperable.  They
are basically designed to identify the user by username and password,
to transfer the mail from server to PC or workstation and to delete the
mail transferred.  It is assumed that SMTP will be used to send mail.
Messages can be retrieved individually, but the only information you
can get about a message without transferring it is its length in
bytes-- useful for PCs with limited storage.

POP2 and POP3 are still used a good deal.  POP3 has a couple of
optional extensions: one to avoid sending passwords, and one to aid in
reading bulletin boards.

IMAP2, IMAP3:  The IMAP family is similar to the POP family, but also
gives clients a way to do string searches through mail that still
resides on the server.  This is designed to allow the PC or workstation
to be more selective as to which mail will be transferred.  The POP
protocols, on the other hand, are designed for simpler server
software.

IMAP2 is used quite a bit.  IMAP3 is an incompatible offshoot that has
not been implemented much.  Recent work not yet documented in an RFC
has extended IMAP2 to include support for multimedia mail.

DMSP (aka PCMAIL):  PCs and workstations can use this protocol to both
send and receive mail.  The system is designed around the idea that
each user can own more than one workstation; however, the system
doesn't seem to handle the idea of a "public workstation" very well.
The PCs and workstations are assumed to hold state information about
the mail, a directory so to speak, and when the PC or workstation is
connected to the server, this directory is updated to "reality".

Issue of Remote Access: Modern commercial e-mail packages typically
have features designed to assist in remote access of ones e-mail.
Features include:
-ability to download mail through a modem
-ability to synchronize two different systems which you are using to
  read your e-mail by plugging them together.
Any method of reading e-mail using PCs or Macintoshes can be used
remotely via the "PCanywhere(tm)" method, e.g. by dialing up your own
office PC and using one of the several kinds of software that allow you
to control your PC over the phone.  Also, any LAN-based method can be
used by using one of the several methods of providing the same protocol
support over dialup lines as are on LANs (SLIP or PPP for the
above-mentioned, TCP/IP-based protocols, ARA for Appletalk-based
protocols, etc, and sometimes using two different protocols, one
incapsulated in the other) under the constraint that any operations
that use the network will be much slower.  Also, POP3 is often used
directly over modems (for example, Eudora can be used in this manner).
The ideal protocol for remote access would not penalize the user for
the much slower communications speed (usually slower by a factor of
100: note that a lot of LAN-based software was written without regard
to minimizing the necessary communication, thus is really hurt by such
slow speeds), yet would allow the same software to run both remotely
and locally, with a wonderful user interface.  It would also not be
overly expensive in communications equipment or services.  This is a
difficult set of objectives and the above-three protocols can achieve
some of them for some users, but what they actually achieve depends a
lot on the user's pattern of e-mail usage.  If a user reads just a
small amount of mail, then we would not worry about the length of time
necessary to download it remotely with POP3, but if the person receives
a lot of mail, but just wants to read a small amount of it at home,
then with IMAP2, they could pick and choose what to read, eliminating
some download time.  If someone is paying for the telephone line time
(possibly the user if it is a long distance call; in any case, the
institution pays a monthly fee for each line it offers, which is
dependent upon how many users it is serving, how often they call, and
how long their calls are) then IMAP2's natural method of usage which
requires the phone call to remain while a user is reading, poking
around, sending, and rearranging mail can be much more costly than
using POP3 if one call is used to quickly download all the mail and
another later call is used to send any replies.  Thus with POP3 a user
might have two 1 minute calls before and after a 30 minute e-mail
session instead of keeping the call for 30 minutes with IMAP2, and each
phone line the institution offers could be serving 15 times as many
such users who would each pay a lot less in long-distance phone bills.

More about the protocols:

Name:      Post Office Protocol, Version 2
Nickname:  POP2
Document:  RFC 937 (Butler et al, February 1985)
TCP-port:  109
Sites:

Name:      Post Office Portocol, Version 3
Nickname:  POP3
Document:  RFC 1460 (Rose, May 1993)
TCP-port:  110 (109 also often used)
Sites:     UC Irvine, MIT

Name:      Distributed Mail Service Protocol
Nickname:  DMSP, Pcmail
Document:  RFC 1056 (Lambert, June 1988)
TCP-port:  158
Sites:     MIT

Name:      Interactive Mail Access Protocol, Version 2
Nickname:  IMAP2
Document:  RFC 1176 (Crispin, August 1990)
TCP-port:  143
Sites:     Stanford, U Washington

Name:      Interactive Mail Access Protocol, Version 2 bis 
Nickname:  IMAP2bis
Document:  ?
TCP-port:  143
Sites:     U Washington

Name:      Interactive Mail Access Protocol, Version 3
Nickname:  IMAP3
Document:  RFC 1203 (Rice, February 1991)
TCP-port:  220
Sites:     Stanford

Implementations:
 
Prot   Computer    Implementation      End     Source
------ ----------- ------------------- ------- --------------------------------
DMSP   PC          pc-epsilon (3.1)    client  allspice.lcs.mit.edu
DMSP   PC          pc-netmail (3.1)    client  allspice.lcs.mit.edu
DMSP   PC          pc-reader           client  allspice.lcs.mit.edu
DMSP   Unix        Pcmail 3.1 reposit. server  allspice.lcs.mit.edu
DMSP   Unix/EMACS  Pcmail 4.2          client  allspice.lcs.mit.edu
DMSP   PC          PC/TCP              client  FTP Software
DMSP   OS/2        PC/TCP              client  FTP Software
DMSP   OS/2        TCP/2               client  Essex Systems
DMSP   OS/2        TCP/2 SERVER PACK   server  Essex Systems
DMSP   OS/2        TCP/2 ADV CLIENT    client  Essex Systems
IMAP2  Macintosh   MacMS 2.2.1         client  sumex-aim.stanford.edu 10/15/93
IMAP2B Macintosh   Mailstrom 1.04      client  sumex-aim.stanford.edu 10/19/93
IMAP2B Macintosh   Mailstrom 2 (b?)    client  sumex-aim.stanford.edu 10/19/93	
POP2   Macintosh   MacPOP 1.5          client  trident.arc.nasa.gov
POP2   MS-DOS      PC POP 2.1          client  trident.arc.nasa.gov
POP3   Macintosh   TCP/Connect II      client  InterCon Systems Corporation
IMAP2  NeXT        EasyMail            client  ftp.cac.washington.edu
IMAP2  NeXT        MailManager         server  ftp.cac.washington.edu
IMAP2  TOPS20      ?                   server  ?
IMAP2  Unix        imap kit            server  ftp.cac.washington.edu
POP23  Unix        imap kit            server  ftp.cac.washington.edu
IMAP2  Unix        Pine 3.07           client  ftp.cac.washington.edu
POP3   Macintosh   Eudora 1.3.1        client  ftp.qualcomm.com 11/2/93
POP3   Macintosh   Eudora 1.4          client  ftp.qualcomm.com 11/2/93
POP3   Macintosh   Eudora 1.4.1 (beta) client  ftp.qualcomm.com 11/2/93
POP3m  Macintosh   Eudora 2.0 (in dev) client  ?
POP3   MS-WINwf    Eudora 1.0.1        client  ftp.qualcomm.com 9/21/93
POP3   MS-WINw     Eudora 1.4b17       client  ftp.qualcomm.com 11/2/93
POP3   MS-WINw     Eudora 2.0a14       client  ? 11/2/93

IMAP2  Unix        ?                   client  ftp.cac.washington.edu
IMAP2  Unix        imapd 3.1           server  sumex-aim.stanford.edu*
IMAP2  Unix/X      ximap 0.7.2         client  sumex-aim.stanford.edu
IMAP2  MS-DOSl+    PC-Pine (beta)      client  pine@cac.washington.edu
IMAP2  Xrx Lsp Mch ?                   client  ?
IMAP2  MS-WIN      ECS (beta)          client  ISA, ftp.srv.ualberta.ca
POP2   Macintosh   POPMail II          client  boombox.micro.umn.edu
POP    Macintosh   POPMail II 2.09     client  boombox? 9/21/93
POP2   Macintosh   POPMail II 2.09     client  boombox? 9/21/93
POP3   Macintosh   POPMail II 2.09     client  boombox? 9/21/93
IMAP2  Macintosh   POPMail II 2.09     client  boombox? 9/21/93
POP2   Macintosh   MailStop            server  boombox.micro.umn.edu
POP2   MS-DOS      LifeLine Mail       client  SunSelect
POP2   MS-DOSk     ?                   server  ucsd.edu
POP2   MS-DOSk     ?                   server  boombox.micro.umn.edu
POP3   MS-DOSk     pop3serv            server  biochemistry.crwu.edu
POP2   MS-DOS      MD/DOS-IP           client  U Maryland
POP2   MS-DOS      PC/TCP              client  FTP Software
POP2   OS/2        PC/TCP for OS/2     client  FTP Software 11/2/93
POP23  MS-DOSp     POPmail/PC 3.0      client  boombox.micro.umn.edu 11/2/93
POP3   MS-DOS?     Minuet (beta)       client  boombox.micro.unm.edu 11/2/93
IMAP?  MS-DOSp     POPmail/PC 3.0      client  boombox.micro.umn.edu
POP?   MS-WINls    TCPMail             client  Pinesoft (pinesoft@net.com)
POP2   Unix        POPmail/unix        server  boombox.micro.umn.edu
POP2   Unix        popd (USC-ISI)      server  trident.arc.nasa.gov
POP2   Unix        imapd/ipop2d        server  ftp.cac.washington.edu
POP23k Unix        mh-6.7 (UCI RandMH) both    ftp.cc.berkeley.edu
POP?   Unix        zmail               client  Z-Code Software (info@z-code.com)
POP23k UnixX       xmh/mh              client  ?
POP23k UnixX       dxmail/mh           client  DEC
POP2   VM          FAL                 server  IBM
POP2   VM          ?                   server  Texas Tech University
POP2   OS/2        TCP/2 SERVER PACK   server  Essex Systems
POP2   VMS         MULTINet            server  TGV, Inc.
POP2   HP3000/MPE  NetMail/3000        server  3K Associates
POP3k  Macintosh   Eudora X            client  ftp.brown.edu
POP3   Macintosh   MacPOP (Berkeley)   client  ftp.cc.berkeley.edu
POP3k  Macintosh   TechMail 2.0        client  net-dist.mit.edu
POP3   Macintosh   MacMH               client  jessica.stanford.edu/info
POP3   Macintosh   POPMail II          client  boombox.micro.umn.edu
POP3   Macintosh   MailStop (soon)     server  UMinn
POP3   Macintosh   VersaTerm Link      client  Synergy Software 10/8/93
POP3   Macintosh   LeeMail 2.0.2 (shw) client  chs.cusd.claremont.edu 10/12/93
POP3t  Unix        popper-1.7          server  ftp.cc.berkeley.edu 10/15/93
POP3k  Unix        popper-1.7k         server  ftp.brown.edu
POP3   Unix        popper-1.831        server  ? 
POP3   Solaris2.X  popper-1.831 mod    server  ftp.uoregon.edu 10/19/93
POP3k  Unix        mh-6.7 (UCI RandMH) both    ics.uci.edu
POP3   Unix        imapd/ipop3d        server  ftp.cac.washington.edu
POP3t  MS-DOSnpo   PC/TCP              client  FTP Software
POP3   OS/2        PC/TCP for OS/2     client  FTP Software 11/2/93
POP3   MS-DOS      TechMail(future)    client  ? 
POP3   MS-DOS      ?                   client  logos.ucs.indiana.edu
POP3   MS-DOSp     NuPOP 1.03          client  ftp.acns.nwu.edu 10/26/93
POP3   MS-DOSp     NuPOP 2.00 (beta)   client  ftp.acns.nwu.edu 9/21/93
POP3   MS-WIN      Pceudora            client  ftp.qualcomm.com 9/24/93
POP3   ?           POPgate (Pmail gw)  client  risc.ua.edu 9/24/93
POP3   MS-DOSl     PMPOP (Pmail gw)    client  risc.ua.edu 10/20/93
POP3x  MS-WIN      WinQVT (2.1)        client  QPC Software (shareware)
POP3   MS-WINp     wnqvtnet 3.0        client  ftp.cica.indiana.edu
POP3   MS-WIN      Open Systems Mail   client  Pine Software
POP3   VMS         IUPOP3 (1.7) (1.6?) server  logos.ucs.indiana.edu
POP3   VMS         MULTINet            both    TGV, Inc.
POP?   VMS         PMDF 4.2            server  Innosoft
IMAP?  VMS         PMDF 4.2            server  Innosoft
POP3   OS/2        TCP/2 SERVER PACK   server  Essex Systems
POP3   OS/2        TCP/2 ADV CLIENT    client  Essex Systems
POP?   MS-DOS      UCDmail             client  ucdavis.ucdavis.edu
POP?   MS-DOS      PC POP              client  ?Bill Schweickert/Sterling Fed
POP?   MS-WINnpo   Super-TCP for Wndws client  Frontier Technologies 10/26/93
POP?   MS-WIN      Windows ELM         client  lister.cc.ic.ac.uk 11/2/93
POP?   MS-DOSni    ChameleonNFS        client  NetManage
POP?   Macintosh   MEWS                client  ?
POP?   Macintosh   byupopmail          client  ?
POP?   VM          ?                   server  TTUVM1
?      Macintosh   Hypermail           ?       ?
------ ----------- ------------------- ------- --------------------------------
Appendix:
Some other packages for desktop systems
------ ----------- ------------------- ------- --------------------------------
uucp   Macintosh   uAccess             peer    Intecom [12/17/92]
SMTP   Macintosh   LeeMail 1.2.4       peer    Shareware, laf@mitre.org
SMTP   Macintosh   LeeMail 2.0.2 (shw) peer    chs.cusd.claremont.edu 10/12/93
SMTP   MS-DOSni    ChameleonNFS        peel    NetManage
uucp   Macintosh   FernMail            peer    Shareware, dplatt@snulbug.mtview.ca.us
prop   Macintosh   MacPost             both    ftp.lu.se 10/19/93
uucp   Macintosh   Eudora 1.3.1        peer    ftp.qualcomm.com
uucp   Macintosh   UUPC                peer    dplatt@snulbug.mtview.ca.us
uucp   Macintosh   gnuucp              peer    jim@fpr.com
uucp   MS-DOS      waffle              peer    ?
uucp   MS-DOS      UUPC                peer    ?
?      MS-Windows  Pegasus/Win 1.02    client  risc.ua.edu 10/5/93
?      MS-DOS      Pegasus/DOS 3.01    client  risc.ua.edu 10/5/93
?      Macintosh   Pegasus/Mac 2.04    client  risc.ua.edu 10/5/93
SMTP   MS-DOS      Charon              gateway risc.ua.edu 10/15/93
------ ----------- ------------------- ------- --------------------------------
Other issues:
(1) What are the common extensions to POP3 and which clients/servers
 support them?
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.
(2) 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-WIN? - similar
MS-WINw - WinSock compliaint
------ ----------- ------------------- ------- --------------------------------