gordanbobich.net
Date: Thu Nov 01 2007 - 11:41:03 CDT

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On Thu, 1 Nov 2007, Wietse Venema wrote:

>>>> 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.
>
> What's the TTL in the SOA record for the domain in question?

A day, IIRC. But the DNS was set some time ago, I can't see how it could
be DNS cache not having expired.

Gordan

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