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From: Murray.pa@XEROX.COM.UUCP
Newsgroups: mod.protocols.tcp-ip
Subject: Re: Adaptive SMTP Timeouts
Message-ID: <860602-175604-178@Xerox>
Date: Mon, 2-Jun-86 15:03:42 EDT
Article-I.D.: Xerox.860602-175604-178
Posted: Mon Jun  2 15:03:42 1986
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An idea that we have found very helpful...

Our mailer keeps outgoing mail sorted by host. Hosts are split into two
categories: healthy and sick. While there is work to do on the healthy
queue, the mailer ignores the sick hosts. Whenever the mailer empties
the healthy queue, it tries the host on the front of the sick queue. (If
that fails, it gets moved to the end of the sick queue.) The idea is to
avoid having the mailer bang its head against hosts that are known to be
causing trouble.

Occasionally mail to a host that isn't really very sick takes much
longer that we would like. This happens when the sick queue is very long
and the mailer is busy so the sick queue doesn't turn over very fast. So
far, this hasn't bothered us enough to do anything about it.

Along the same lines, we also keep mail to a host sorted, but not quite
chronologically. Whenever the mailer tries to send a message and fails,
that message gets moved to the end of the queue. Occasionally, this lets
the rest of the mail get through when one particular message is
having/causing troubles.