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10 Issue of Remote Access (LAN Mail Protocols)




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This article is from the LAN Mail Protocols FAQ, by John Wobus jmwobus@syr.edu with numerous contributions by others.

10 Issue of Remote Access (LAN Mail Protocols)

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 remote control (the "PCanywhere(tm)" method, e.g. by
dialing up your own office PC/Macintosh and using one of the several
kinds of software that allow you to control your PC/Macintosh 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 sometime 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 IMAP4, 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 IMAP4'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 IMAP4, 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. Note that with the advent of multimedia mail (see MIME below)
whose messages can be very large, it is possible that downloading even
one message that you end up not reading remotely could ruin such a
nice-sounding scenario.

Note that with the growth of Internet Service Providers, remote access
is becoming the normal way for many people to do their e-mail, and
offering such services is one of the major growth areas for POP and
IMAP.

 

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