Newsgroups: comp.archives
Path: utzoo!utgpu!news-server.csri.toronto.edu!ox.com!emv
From: mrc@Tomobiki-Cho.CAC.Washington.EDU (Mark Crispin)
Subject: [tcp-ip] Re: POP protocol
Message-ID: <1991Jan3.022621.10417@ox.com>
Followup-To: comp.protocols.tcp-ip
Sender: emv@ox.com (Edward Vielmetti)
Reply-To: mrc@Tomobiki-Cho.CAC.Washington.EDU (Mark Crispin)
Organization: Mendou Zaibatsu, Tomobiki-Cho, Butsumetsu-Shi
References: <E9633327E93FE1EE45@vaxsar.bitnet> <13669@milton.u.washington.edu>
Date: Thu, 3 Jan 91 02:26:21 GMT
Approved: emv@ox.com (Edward Vielmetti)
X-Original-Newsgroups: comp.protocols.tcp-ip

Archive-name: mail/imap/imap/1991-01-02
Archive: ftphost.cac.washington.edu:/imap/imap.tar.Z [128.95.112.1]
Original-posting-by: mrc@Tomobiki-Cho.CAC.Washington.EDU (Mark Crispin)
Original-subject: Re: POP protocol
Reposted-by: emv@ox.com (Edward Vielmetti)

In article <E9633327E93FE1EE45@vaxsar.bitnet> BIWINE@VAXSAR.VASSAR.EDU (Bill Wine) writes:
>Our concern is that the POP architecture
>may not be sutiable for a large mail system.  It seems inefficient for
>the POP client to check for newmail every 5 or 10 minutes.
>It seems to me that a
>better idea would be for a client to log in once, and for the server
>to check for newmail periodically, then send it to the client.  

There is no way that I am aware of in either the POP2 or the POP3
protocol for a client to check for new mail; the only way is to close
the POP connection and open a new one.  There are some auxillary
protocols to "check for new mail", some of which I believe are UDP
based.

>Would anyone care to share their experiences with large Mac or PC
>e-mail systems (100+ concurrent users).  Is the POP architecture
>suitable for large systems?  Is there a better one?

An alternative to the POP protocols is the IMAP protocol (RFC-1176).
IMAP provides both an explicit "check for new mail" and server-
controlled new mail notification.

You can get a distribution package on FTPHOST.CAC.WASHINGTON.EDU (IP
address 128.95.112.1) as imap/imap.tar.Z via anonymous FTP.  Stanford
has written a Mac client.  I wrote a NeXT and generic Unix client; I'm
working on a PC client for IMAP now.  The IMAP distribution also
includes a POP2 and POP3 server so you can leverage on your existing
POP software without incompatibilities (the underlying mail access
library is the same in all cases); the POP servers can also be IMAP
clients so any POP clients can access IMAP servers.

Whether you choose IMAP or POP depends a lot upon what you are trying
to do.  They are often mistakenly thought of as competing protocols,
but really have different functionalities.  POP is for downloading an
RFC-822 format mailbox to a client, whereas IMAP is for a client to
manage and retrieve data on a remote mailbox maintained on a server.

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