Today, messages can just disappear on the way to the user's mailbox
(often at or after that last-hop MTA). They do so without NDNs out
of fear of blowback, and they do so for two main reasons. ...
You know, DNSBLs make mystery disappearances less likely, not more.
The DNSBLs that most people use are typically checked at SMTP time, sp
MTAs can give a 5xx rejection using the TXT record from the DNSBL that
identifies why the mail was rejected. Even if the DNSBL isn't in the
rejection message, there aren't that many lists that are widely enough
used to matter, and since DNSBL listings (unlike the private
per-system blacklists that are the most likely alternative) are by
their nature public, it is easy enough to check a bunch of them and
see if you're on one of them, thereby identifying the problem. The
other approach is to use them in a scoring filter, but they'll do what
they do whether or not they mix DNSBLs into the score.
Unlike you, I don't see "overwhelming community consensus for
Aw, come on. There's a billion and a half mailboxes using the
Spamhaus DNSBLs, on systems ranging from giant ISPs down to hobbyist
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