From: (no name) (no email)
Date: Thu Nov 01 2007 - 11:51:15 EDT
On Thu, 1 Nov 2007, Wietse Venema wrote:
> :
>>> I have one suggestion.
>>>
>>> Point Postfix to a DNS server that doesn't truncate replies, and
>>> show evidence that Postfix behaves incorrectly. If so, we will
>>> investigate and may even ask you to turn on debug logging.
>>
>> The DNS is _only_ truncating the additional section. It is NOT truncating
>> the main section, regardless of how big it is.
>>
>>> Postfix doesn't cut corners; it takes the MX list and then does
>>> separate A lookups for each of them. If something is cutting corners
>>> here it is more likely that DNS server that is truncating your
>>> replies, and that does who knows what with the partial information.
>>> I am, however, not interested in adding code to Postfix to work
>>> around mis-behaving DNS servers.
>>
>> Agreed, this would be bad. If Postfix does separate lookups then DNS is
>> not the problem, as the main section is always returned correctly.
>
> Postfix ignores the additional A records, but the broken DNS server
> will cache them.
>
> The question then is what happens with the A records that were
> chopped off. Perhaps the broken DNS server assumes that those
> records don't exist? Usually, all the MX's A records are included
> as additional information. If the broken DNS server assumes that
> "record not present in additional information" means "record does
> not exist", then we have an explanation for the erratic behavior
> you observe.
>
> You can test this by hand, by the way. First look up the MX records,
> then see what A replies you get for each MX host.
That was my first thought, and it was tested, re-tested, and then tested
again - the DNS is listing all the MX-records, and each MX host gets
looked up with the correct address.
Gordan
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