On Wed, Jan 15, 2020 at 07:16:30PM -0500, Michael Orlitzky wrote:

> I'd like to bounce these immediately as a courtesy to the sender.
> Blacklisting typo domains is a (technically incorrect) losing battle,
> and if the message is to a distribution list, then it's useful for the
> sender to know that the recipient is dead.

On the other hand, likely or existing typo-squatter domains, especially
if they (almost) match your own domain, or the domain of a client or
business partner, can be vehicles for costly data leaks.  A few
incorrect bounces may be quite acceptable collateral risk of preventing
known potential harm.

> Yes, they'd get the bounce anyway when the message expires. But if I've
> already done the thinkative work to figure out that the message will
> bounce, it's a win at zero cost to bounce it immediately.

This is tricky for multi-recipient mail, where different deferred
recipients may have different error reasons.  So overriding the error
message is generally wrong, you'd go with the errors already saved for
each recipient.

Therefore, if this were to be made possible, the right mechanism would
be to to somehow expedite message expiration, with normal processing
on message expiration happening earlier than it would otherwise.

This could be done by adding a place-holder record to the queue file,
that could be later atomically (one byte write) updated to indicate
that the message is administratively expired.  Such messages would
expire after the next delivery attempt and would not be deferred


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