On 3 Feb 2020, at 14:20, Michael Orlitzky via mailop wrote:
You have problems with 100% of messages 0.0001% of the time -- it's
not
a steady 99.9999 success rate, even though that's what the numbers
look
like if your window is five-years long.
Since recently – heh, let's call it 5-6 years – I've observed more
and more that senders are unable to connect the first NDR ("your mail is
stuck, we're still trying") with their original message. There's some
cognitive dissonance at play here. If the bounce is not instantaneous,
that NDR is a waste of resources for them. More or less the same happens
with the final NDR ("sorry, I give up"), where they seem to be unable to
grasp that the message was not delivered.
Setting the first NDR too soon tend to cause confusion – and often, a
resent of the same message – which does not improve the situation for
that specific communication.
This issue is, IMO, testament that the email landscape today is far more
resilient than 30 years ago. But we still need to accommodate the
occasional flooded rack. User expectations are very heavily driven by
what happens with 99.9999% of their email. Can't say I blame them.
Personally, I've seen more bounces in the last 3 months due to receivers
wanting to do TLSv1.0 than the rest of possible causes, all together.
The NDR has helped notice this and make special arrangements. But still,
the senders were not entirely aware of what happened to their email
during the few hours they remained in our outbound queues.
Best regards
-lem
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