gordanbobich.net
Date: Thu Nov 01 2007 - 10:53:48 CDT

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On Thu, 1 Nov 2007, Wietse Venema wrote:

> gordanbobich.net:
>> Sure - and I've gone one better and hidden my real MX somewhere between
>> the rejecting ones at the top (which leads to immediate retries to the
>> next MX down, which may or may not do the same thing), and the tarpitting
>> ones at the bottom. And even if a valid MTA gets to the bottom ones
>> through a minor network outage, it'll still eventually time out and roll
>> over to retry from the top after a little while.
>
> The RFC does not require that an SMTP client tries every MX host.
> It only requires two. If you list lots of non-responding MX hosts
> then you can expect interoperability problems.

Sure - but if the top two were tried in the correct order, this problem
wouldn't have happened, and if I saw it give up after two, I'd not be
asking why it started at the 16th and didn't go from there for 5 hours.

> Postfix will not connect to all MX hosts, because that is a way
> for bad guys to DOS a server.

Great! So I won't tarpit any postfix machines, then. :-)
But as I said, that's not the problem here.

Gordan

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