On Mon, 30 Sep 2024, Quelrond wrote:
Thanks a lot for this clarification.
We contacted our ISP, this is their intentional drop, the don't want to
deliver any mail with empty 'From' field, we cannot do anything with it.
We need to send NDR though ;)
Your ISP does not have anything to do with this. Unless you hired them
to run email for you - in which case, why are you here?
They cannot do deep packet inspection to block NDR of any description
when there is a TLS connection to the recipient.
Are you attempting to relay mail through your ISP? Why? If they
block outgoing port 25 to force you to relay mail through them, then maybe
you need to upgrade to "business" or something (e.g. Cox doesn't allow
outgoing SMTP for consumer accounts). Or you need a new ISP. In the
mean time, rent a small vps and run opensmtpd to relay mail (remember to
update SPF policy).
Is there any way to configure OpenSMTPD to send NDR using another SMTP
relay, or directly? Ideally - send all NDR directly, but we can list the
This suggests you are using your ISP as an SMTP relay. Don't. You had
to explicity mention their relay in your existing config - or maybe
they redirect outgoing port 25 to their relay, and you are back to
upgrading to business account, new ISP, rent a vps for relay through
a vpn to bypass their block, or hire an SMTP relay service (which must
be accessed through a vpn to bypass the block).
