[dns-operations] Why would an MTA issue an ANY query instead of an MX query?

[DTNX Postmaster]

On Jun 10, 2012, at 16:23, Paul Vixie wrote:

> On 2012-06-10 12:59 PM, Patrick W. Gilmore wrote:
>>>> A single ANY query for a domain gives you the NS, MX, TXT and SPF records, plus any A/AAAA record present. At scale, who knows, the reduction in number of queries probably adds up.
>>> 
>>> It strikes me as laziness and cost-shifting.
>> 
>> If you need to do multiple queries (e.g. TXT & MX), is it better for either side to do two queries instead of one?
> 
> yes, since the queries can be transmitted simultaneously, and there's way less risk of TC=1 and followup TCP.

Interesting, I did not know that. Does that mean that even from the 
perspective of a SMTP server, which may need between three and five 
queries, it may be more efficient to do seperate queries instead of
a single, large ANY query?

Cya,
Jona