It was suggested to me that an SMTP server implementing greylisting
needs to return a descriptive code, and some variant on
450 4.7.1 You've been greylisted, try again later
is the "best fit" from RFC3463, which says:
X.7.1 Delivery not authorized, message refused
The sender is not authorized to send to the destination. This
can be the result of per-host or per-recipient filtering. This
memo does not discuss the merits of any such filtering, but
provides a mechanism to report such.
Yep. Stick a 4 on it to tell the other end that it's not authorized *now*,
but might be later, and we're ready to rock. Unfortunately, there's one
final line to that description:
This is useful only as a
permanent error.
What's the general consensus here? Is 4.7.1 in fact useful as a temporary
error in this case, or do we risk the wrath of the RFC wonks if stuff deploys
that uses that?
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