[exim] exim rewrite envelope-from for one router only

Hi. This one has got me completely stumped. Any tips would be very much
appreciated :)

I need to rewrite the SMTP-From header for /etc/alias type redirects.

This is to avoid upsetting the SPF checker on the next mail gateway (for
external users mailing into one of my aliases).

I would like to do what mailman does and replace the SMTP-From with
something like:

my-alias[-bounces]@mydomain.example.com
for the redirect of the same name.


OK - You can headers_add in a router so changing From: and Reply-To:
headers is simple enough...

But I can see no way to change the SMTP-From/Envelope-From within a
router or indeed anywhere using the same conditions the router triggers on.

This is for Departmental contact addresses, where running a full mailman
list for 2-15 recipients is a bit inelegant.

I've tried *conditional* rewrite rules but to be honest, I've never done
those before and I'm getting in a muddle.

I have considered a systemfilter too, or as someone else suggested off
list, piping to a script. But I feel there must be a way to do this
inside the exim config and I must be missing a trick.

Many thanks,

Tim
--
Tim Watts