Re: [exim] Routing failed deliveries through an ESP

On 2023-04-17 at 03:54:37 UTC-0400 (Mon, 17 Apr 2023 08:54:37 +0100)
Graeme Fowler via Exim-users <graeme@???>
is rumored to have said:

> On 17 April 2023 03:08:29 Lance Lovette via Exim-users
> <exim-users@???> wrote:
>> How might I configure my routers to ignore an initial 5xx response
>> from the
>> first router and attempt another (and maybe future) deliveries
>> through an
>> alternate router?
>
> I'm going to make the very obvious and morally correct answer: you
> don't.
>
> If you get a 5xx error from the receiver's MX, you do the right thing
> and abide by it. They're telling you they didn't want your message.

There's a rational basis for an exception for 5xx before MAIL FROM, when
the target only has the connection parameters and HELO name to use as a
basis for rejection. Re-routing via a fallback path isn't entirely
unjustifiable in that case, as it changes those elements of the
transaction.


> If you've got such a problem with IP or domain reputation that you end
> up on DNSBLs with any frequency, you need to work on that rather than
> palming off your messages to a third party.

Like it or not, DNSBLs are far from the only reason MTAs use to reject
mail. In the case of early 5xx rejections, it is likely that a public
DNSBL is not the mechanism in use. Fixing whatever problem caused a
particular site to get cranky about Linode or OVH or Digital Ocean or
whatever other garbage VPS provider is a problem this month isn't
feasible for their individual customers.

> That said: why not just send via the ESP in the first place?

ESPs come with their own reputational issues. Deliverability for modest
volume non-bulk mail is a difficult problem.



--
Bill Cole
bill@??? or billcole@???
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Not Currently Available For Hire