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Subject: Re: external delivery and network errors
From: Wietse Venema (wietseporcupine.org)
Date: Wed Jun 21 2000 - 16:00:41 CDT

Jon Burman:
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>
> We provide a mail forwarding service for our clients whereby we send email
> addressed to our clients' domains on to the mailboxes they have with their
> dialup providers. Recently another service provider, which provides dialup
> services for a number of our customers, suffered a denial of service attack
> against their mail servers. While they were sorting this problem out they
> denied all access via their routers to their SMTP servers from the offending
> peer networks, including ours.
>
> The next thing we knew our mail servers started to queue all mail. I
> examined the log files and noticed that Postfix was continuously trying to
> connect to the other servers and kept getting "connection refused" errors.
> All other mail to other providers who were not affected just queued up.
> Looking at the documentation I think that Postfix sends mail to mail hosts
> in a round-robin order, but it was never getting as far as round-robining to
> other hosts.

What's your postconf -n output? This sounds like a configuration
problem. Out of the box Postfix does not try continuously to connect
to a dead server, in fact, it remembers that a site is dead and
defers delivery to that site without trying every message.

        Wietse