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

[sthaug at nethelp.no]

> "Not supporting"
> ANY queries would also have side effects - simply dropping the
> query maks the authoritative server appear unresponsive to the
> recursive server initiating the query.

Note that in many cases the server receiving the ANY query is a
recursive server, not an authoritative server.

For instance, the ISP I work for runs several recursive servers. Those
recursive servers are only available to the ISP's customers. Even so,
those recursive servers are contributing to DDoS attacks - because so
many of the *clients* are either CPEs with a DNS proxy open from the
WAN side, or customers' general open recursive servers which use the
ISP recursive servers as forwarders.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no