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    “ANY” is not a popular query type - no legitimate software uses it (with the notable exception of qmail).

    I couldn’t help but wonder why.

    From www.memoryhole.net/qmail/ :

    Once upon a time, back in 1996, there was a really unfortunate bug in the most popular DNS server software (BIND 4.9.3): it did not respond correctly to “CNAME” requests (that is to say, requests for any CNAME data about a particular domain name). This is critical information that an email server needs to know to do its job. Thankfully, there was a way to work around the problem: “ANY” requests. These requests ask the DNS server, essentially, for any and ALL information it has about the domain name in question, including CNAME information.

    A different explanation, from https://fanf.livejournal.com/122220.html :

    There is exactly one point where it makes this query, which is when it is doing domain canonicalization of the envelope of outgoing messages. This is as specified by RFC 1123 section 5.2.2. However this requirement is obsolete and modern MTAs don’t do it. You could fix qmail’s ANY query bugs by just deleting the canonicalization code.

    The qmail 1.03 CHANGES file doesn’t mention ANY, so I guess it still makes these queries.

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      Another vestige of the old trusting internet is gone. RIP. :(

      It’ll join the ranks of telnetting to port 25 to debug a mail server, or 80 to debug a web server :)