On 2023-04-17 at 03:54:37 UTC-0400 (Mon, 17 Apr 2023 08:54:37 +0100)
Graeme Fowler via Exim-users <gra...@graemef.net>
is rumored to have said:
On 17 April 2023 03:08:29 Lance Lovette via Exim-users
<exim-users@exim.org> 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
b...@scconsult.com or billc...@apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Not Currently Available For Hire
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