RE: [exim] router for bounces

Hi.

> I have access to two smart hosts, i only want to use one of them for
> delivering my bounce messages (post exiscan of course)

Now days generating bounces is a *bad* behavior. If you do not want the
message, you *should* (not must, but should) avoid bouncing in favor of
SMTP 55x, no matter how, after RCPT or DATA or even HELO.

That's just an advice, but nothing more.

> Is the proper approach to add a header the message upon error, and
> when it comes to to for the transport to be chosen to look for that
> header?

Your bounces are:
1) Having empty sender.
2) Generated by your host (locally).

So, both $sender_address and $sender_host_address are empty for *your*
locally-generated bounces. Do not mess them with foreign bounces.
I consider using headers as a bad idea, because they can be forged and
your system could be more likely abused (compromised). I could be wrong
though.