This is pretty effective from Verizon's viewpoint, but bombards any
forged domains with HELO/MAIL FROM:<>/RCPT TO:<...>/QUIT, which some
of those domains interpret as an attack.
However if an explicit SMTP callback mechanism existed it might make a very
valuable contribution.
One idea I first discussed a year or two ago is that you could use ETRN to
temporarily reject mail with a 4xx, then use ETRN to fetch it.
If you don't want it, premanently reject it with a 5xx when the sending MTA
retries.
Extend ETRN to allow it to be used to specify which sender and recipient
you are ready to accept. I'm rusty and busy.. perhaps it already does this.
Add a command to allow you to say that you will not receive mail for, or
from some entity (host, domain, user) for some period.
During the time you free up you can do all kinds of checks, at your
leisure.
d.
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