[Exim] Trying to implement user+extension@domain in envelope…

Hello,

I've been trying to properly implement user+extension@domain parsing in exim
for the last two days with very limited success.

The delivery and transport for inbound smtp mail is easy to deal with, and
somewhat covered by the FAQ. That should be working correctly (mail to
hmh+eximml@??? arriving in the system is being correctly handled and
delivered to user hmh).

I still have two problems left:

1. I need exim to accept mail from _untrusted_ users using From:
user+whatever@domain, as it is a perfectly valid source address now and I
can't have exim adding Sender: user@domain headers. Also, I need this to
work from both smtp and local (delivered through the "sendmail" command
implemented by exim) sources.

I couldn't find a way to do this, and the FAQ didn't help much :-(

2. I need the _envelope_ sender to be properly set to user+whatever for
outgoing mail from user+whatever@domain. And I need this to work from
smtp and local ("sendmail" command) sources.

I've tried rewrites. No good, I can't request a From: line to rewrite a
envelope sender.

I've tried return_path= and some assorted transport tricks. No good, exim
does all fancy sender verification (which is causing me problems, as I
haven't figured out how to do 1. above yet), but seems not to expose this
to the configuration file so I simply couldn't find a way to get the
RFC-822 sender from the message to fix the envelope.

Is there another way to do this without ressorting to filtering the mail
through an external script ? I apologise if this is a FAQ, but I couldn't
find a working answer there...

--
Henrique Holschuh