On 2023-08-22, Mark Elkins via Exim-users <exim-users@???> wrote:
> Hi Exim Users,
>
> I'm looking for advice on Grey Listing vs outlook.com's behaviour of
> retrying to send from multiple SMTP relays.
>
> Many years ago, we added Grey Listing as a feature to Exim. This delays
> the receiving of new emails by 10 minutes, so the next try will usually
> work but allow for that combination to be properly black-listed - if
> required. This is done by saving the tuple of information, From, To,
> SMTP_Relay. I usually save it for 12 months.
>
> This usually works well - initial emails are delayed by 15 minutes - no
> one complains.
>
> However, emails via Microsoft will keep changing the identity of the
> SMTP_Relay to a group of 10 or so SMTP Servers, so the initial delay
> keeps getting implemented ==> Customers complain.
>
> I could:-
>
> 1 - Remove grey Listing - but it used to have a purpose and I assume
> still has?
>
> 2 - Remove the SMTP-Server element from Grey Listing - but it was put
> there for a reason?
>
> 3 - White list all the Outlook.com SMTP Server addresses - do they
> though remain static?
>
> What do people advise?
>
> If No. 3, anyone have a definitive list to WhiteList with? Perhaps a
> link to a dynamic WhiteList?
perhaps you could use their SPF record as a source of truth.
I can't think of a pure exim way to automate that though, because
senders will be using non-outlook domains.
By the way; gmail, yahoo, sendgrid: same deal.
--
Jasen.
🇺🇦 Слава Україні
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