Michael, I was with you until it was revealed you mention a blacklist in your
response. Sendgrid assumes that the words in the response actually have
something to do with the reason it's being temporarily rejected, which is a fair
assumption to make even if it doesn't follow spec. Then using different retry
logic based on that reason does make sense at that scale. I mean effort wise,
not "we're big so we can do whatever we want" wise. I'm personally no fan of
them, but I don't think this behaviour specifically is odd at all.
Louis
Op zaterdag 24 juni 2023 om 10:42, schreef Andy Smith via mailop:
> Hello,
>
> On Fri, Jun 23, 2023 at 11:13:56PM -0500, Al Iverson via mailop wrote:
> > What if we just got to the heart of the matter and admitted that
> > greylisting is useless 2023?
>
> For me that isn't the heart of the matter. I mean it's an
> interesting discussion still, but what surprised me about this
> discussion is how easy it is to unwittingly hit one of SendGrid's
> heuristics here.
>
> In the specific case at hand it seems that the OP is greylisting
> SendGrid for being on some sort of blocklist, and the specific
> mention of "blacklist" in the 4xx response is hitting a SendGrid
> heuristic that says "don't bother to retry these", so messages are
> actually being lost. I think it has implications beyond greylisting.
>
> When it comes down to SMTP responses I used to be more on the side
> of including verbose text as to reasoning rather than just a terse
> code or a generic message. This turn of events is pushing me towards
> the "terse code" stance because I don't want to unwittingly have my
> 4xx be interpreted in other ways. I'm talking about 4xx that have
> nothing to do with greylisting here.
>
> I wouldn't go as far as to characterise my belief that 4xx should
> always be retried to be as firm as fanaticism or religion. Like I
> say, I can see why in some specific cases large senders might not
> want to. The combination of seeing 4xx and "blacklist" being enough
> though seems like a pretty blunt tool. I'm surprised at that.
>
> I don't have an appreciation of the scale but are the rewards on
> SendGrid's side really worth the risk? I think if I was doing it I'd
> want to be more specific and maybe even try to also match on
> recipient domain and/or MX IP or ASN or something. It strikes me
> that if there is an actual problem with messages staying in a queue
> for days because of perpetual 4xx it's going to be with large
> mailbox providers not every enthusiast with a Linux box and a
> handful of users.
>
> Cheers,
> Andy
>
> --
> https://bitfolk.com/ [https://bitfolk.com/] -- No-nonsense VPS hosting
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