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From: AI.CLIVE@MCC.COM.UUCP
Newsgroups: mod.protocols.tcp-ip
Subject: Another aspect of SMTP timeouts
Message-ID: <12282419301.20.AI.CLIVE@MCC.COM>
Date: Fri, 27-Feb-87 12:04:18 EST
Article-I.D.: MCC.12282419301.20.AI.CLIVE
Posted: Fri Feb 27 12:04:18 1987
Date-Received: Sun, 1-Mar-87 10:28:59 EST
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The large number of recent messages about SMTP clients waiting for servers
don't seem to have mentioned a related problem which is just as annoying:
How long should an SMTP server process wait for a client before giving up?

For many weeks our system constantly had two or three active server
processes connected to a certain host.  Investigation showed that the
client host would stop sending data after the MAIL FROM: command, and our
SMTP server would give up and close the connection 5 minutes later.  A
minute or two later, the client host would open another connection and try
again, etc. etc.  I finally had to increase the server timeout to FIFTEEN
minutes, and the client was finally able to get the message through.

People have suggested several reasons why a server might be delayed in
responding to a client; but I see no excuse for a client to be so slow
about it.  The host in question was an overloaded 750 running Unix.  I
don't know many more details, but I'm told that the Unix mailer actually
validates each address in the header after the connection is already open,
and that furthermore this validation is repeated during each connection to
the various hosts for which the message is destined.  If a message has a
couple of dozen addressees, this adds up to quite a bit of time.

This sounds unbelievable to me, and I hope that Unix folks take the time to
tell me that my info is wrong, or that the situation will soon be fixed.
Mailers should get all of their validation, etc., done BEFORE opening any
connection.  Once the connection is open they should state their business
quickly, expect a quick response, and then leave.  A network connection
is a valuable resource, and my system can't afford to tie up several
in an idle state waiting for remote hosts to spin their wheels.

Clive
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