Michael B?ker:
> Thank you rob0, I decided to go with your second suggestion:
>
> > > > 2. Postfix should *only* relay through one of the hosts in
> > > > sender_dependent_relayhost_maps (or deliver locally), and *never*
> > > > try to deliver directly to some external domain's MX.
> >
> > That one could be done with "default_transport = error:not allowed"
> > and replacing sender_dependent_relayhost_maps with
> > sender_dependent_default_transport_maps.
>
> This works as intended. After reading a bit more about error(8) and DSN
> codes, I decided to go with a verbose error message I can recognize:
>
> default_transport = error:5.1.8 no relay for this sender address
>
> For reasons I don't fully understand, postfix' smtpd maps the return DSN
> from 5.1.8 to 5.1.2, but that's not a concern to me.
The SMTP server error response says:
recipient address rejected (plus your free text)
Therefore the DSN code is that for recipient. It's not clever
enough to understand your free text.
To avoid conversion, specify 5.0.0.
Wietse
> Thanks again for your time,
> Michael
>
