> On 21 Nov 2019, at 17:06, Jaroslaw Rafa <r...@rafa.eu.org> wrote:
>
> Dnia 21.11.2019 o godz. 23:50:15 Gregory Heytings pisze:
>> And there are various techniques (for example connection
>> rate limits, response delays, greylisting) that prevent you from
>> "accepting all mail" and that have zero false positives.
>
> As for greylisting, it's no more true now.
>
> Some large and popular mail sending services started some time ago to send
> mail in a way that is incompatible with greylisting. Greylisting assumes
> that after first 4xx reject, the sending server will retry: a) after a few
> minutes; b) from the same IP address. These services: a) retry immediately,
> after 5-10 seconds; b) use different IP address on each retry and c) give up
> after a few unsuccessful attempts. Thus it is possible you never get mail
> sent from these services if you use greylisting.
Not to mention many that never retry at all (seems to be mostly banks).
> WeTransfer is one example of such service. I ran into this issue when
> someone send me files via WeTransfer and I never got the message with
> download links. I checked my Postfix logs and discovered this behaviour.
> Many other websites behave in a similar way, especially ones that use
> Sendgrid to send emails. I also have lost some transactional emails (eg.
> registration confirmation or password reset links) from several websites
> (for example from Spotify) that way.
Amazon round-robins their servers as well.
> I even tried to contact these services and report the problem, but it
> seems that they don't even understand what the problem is.
Worse than that, they believe there is no problem. Or that YOU are the problem.
--
Ninety percent of true love is acute, ear-burning embarrassment. —Wyrd
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