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

bert hubert bert.hubert at netherlabs.nl
Sun Jun 10 20:10:00 UTC 2012

On Jun 10, 2012, at 12:17 PM, Dobbins, Roland wrote:

> Clue appreciated, thanks!

Close reading of RFC 1035 shows that sending RD=1 ANY queries is taking a huge chance.. An ANY RD=1 query to a resolver basically means 'give me what you have in the cache', and if only if you have nothing, go out and ask for ANY from the AUTH servers.

So you might get back an A record only, for example - even though MX records exist. So it is just stupid to do this unless you fall back to an MX query if you get no MX in the answer (and even then..).


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