postfix--- via Postfix-users:
>
> On 2026-07-18 10:52, Wietse Venema via Postfix-users wrote:
> > Wietse Venema via Postfix-users:
> >> In my smtpd_proxy_filter proposal there is no queue on the bastion
> >> host.
> >>
> >> internet -> bastion (postscreen -> smtpd)
> >> -> hidden (smtpd -> cleanup -> queue...)
> >>
> >> This also means no backscatter when the hidden smtpd rejects
> >> some remote client command.
> >
> > Perhap a simpler arrangement is to run HaProxy on the bastion host,
> > talking to a hidden MTA. For availability, run multiple hidden MTAs
> > on different hosts, with internal forwarding to collect mail in one
> > place.
>
> I understand better now, and I understand the use of the word "hidden."
> While "bastion" describes well the cloud node, "hidden" is not
> semantically precise. I have not made up my mind yet, but it is
> possible that the on-premises node will *send* emails. Proxy is not
> what I am looking for, but thank you for making me attentive to this
> possible configuration.
This would be the inbound path:
internet -> cloud (HaProxy or nginx) ->
on-premise (postscreen port 26 -> smtpd -> cleanup -> queue...)
Outbound could be direct from the on-premise MTA if your IP address
has a clean reputation.
Wietse
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