Re: [EAI] Chinese email address

[John C Klensin <[e-mail]>]

--On Wednesday, April 22, 2015 08:07 +0000 Franck Martin
<[e-mail]> wrote:

> Also I notice you require SPF pass to email this domain,
> otherwise you get the error: 450 Requested mail action not
> taken: Invalid IP
> 
> a 450 is a bit bad, either SPF pass or it does not, SPF temp
> failures are rare (but not uncommon) so it should have been a
> 550.

More generally, you should assume that an SMTP sender will
interpret _any_ 4yz code as an indication that it should return
the mail to its queue and try again.   If such a sender is using
the recommended back-off policy for queue management, that will
result in several more attempts in the next several hours before
backing off toward intervals of multiple hours and keeping that
up for days (SMTP requires a minimum of three days).  If you can
reasonably expect the same message envelope, from the same
sender (and address) to be rejected again every time it is
tried, then 4yz codes just add extra costs for both the sender
and recipient sites.  Perhaps more important, it delays any
possibility of the sending user getting notification that the
message did not go through.

    john