On Mon, Aug 07, 2023 at 03:19:59PM -0400, Alex wrote:
> > The only plausible solution on your end is to not queue mail for this
> > domain, but rather proxy it through to the destination, with the
> > response to "." coming from the final downstream systems. This may be
> > possible with:
> >
> > http://www.postfix.org/postconf.5.html#smtpd_proxy_filter
> >
> > provided you can dedicate an IP address (port 25 smtpd(8) instance) for
> > this destination.
>
> So I would do this in place of the transport filter I currently have in
> place?
>
> example.com smtp:mx1.hc4719.iphmx.com
Adding a bit more detail to Wietse's response, you'd need to
substantially change the architecture.
1. The destination domain requires a dedicate smtpd(8) listener, i.e.
a dedicated IP address and corresponding master.cf entry.
2. Your smtpd_proxy_filter must run synchronously with the connected
client, applying whatever processing is needed as the message passes
through it.
3. The proxy filter must stutter the modified SMTP envelope and content
directly to the destination system(s), not back into the Postfix
queue.
It is far from clear this is worth it. But if the customer is paying
enough to make it worth your while, that's what it takes, unless they
are willing to quarantine rather than reject any junk that passes
through your filters.
Don't attempt this until you've tested it with a non-production domain
and fully understood how this is supposed to work.
--
Viktor.
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