On Tue, Nov 19, 2019 at 10:24:30AM +0100, Angel L. Mateo wrote:
> * Mail from @internal1.com and to @external1.com to be relayed through
> relay.provider.com
If internal1.com is just one of your internal domains, and the policy
should apply to just some of your internal users, then this is a policy
that is difficult to address with current Postfix transport resolution
architecture.
About the best one can do is route such mail through two Postfix
instances, the first separates out mail from just that domain sending it
to a second dedicated instance, where the transport for the destination
is the custom value you want.
If there's just one internal domain, then you'd simply route all
internal mail out via a different Postfix MTA than the one used for
inbound mail.
If none of these work for you. You could try Exim. While it has had a
run of security issues lately, and I personally dislike it for a variety
of reasons, ... it has some built-in customization features not found in
Postfix and probably can express the type of conditions you describe in
its "router" selection logic.
--
Viktor.
