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Re: [ietf-smtp] SMTP Greylisting Retry Hints + PRDR

2019-02-07 11:47:26
On Thu, 07 Feb 2019 10:23:41 -0500, Hector Santos said:

different triplets, and with such a Greylist server, it is assuming 
clients are prepared to behave properly, as expected, to reschedule 

I find the phrase "assuming clients are prepared to behave properly"
rather amusing when we're talking about a technique for dealing
with clients that are maliciously trying to misbehave.

    GreyListing Servers MAY issue multiple and different reply hints per
    RCPT TO in a transaction.

So I can end you a MAIL FROM and 1 RCPT TO, and get back two or
more *different* hints?

1) Why is this at all useful enough to be allowed? What's the use case?

2) Must the hints be on the same line of a 451, or are continuation lines
allowed/required? (I'm willing to bet that even in 2019, multi-line replies to a
RCPT are rare enough that some mail clients *still* get this wrong)

3) If the two hints are different, should the client use the first, the last,
the shortest,the longest, or treat it as "the client must reply inside
this window for the mail to be accepted"?

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