In your previous mail you wrote:
So I'm having trouble guessing why your systems are still seeing
64.170.93.22, much less sending mail to it.
=> a long time ago mail.ietf.org anti-spam dropped SMTP over IPv6
from a MTA address without a PTR. I put a workaround using the IPv4
address (the old one), it was fixed but I didn't remove the
workaround.
I agree that having a system floating around that runs an SMTP
server but that eats messages ("blindly" or not) is undesirable
as an operational policy.
=> exactly and BTW 32.98.170.64.in-addr.arpa has still a PTR to
mail.ietf.org.
Regards
Francis(_dot_)Dupont(_at_)fdupont(_dot_)fr
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