[Exim] Setting the envelope to the From: content

Platform: Intel PII, debian testing/unstable (sarge), exim 3.36

I want to set the envelope sender on outgoing messages to the same as
the content of the From: field in the message being sent.

I've tried doing it, by having the line
return_path = ${local_part:$reply_address}@${domain:$reply_address}
in the remote_smtp transport.

I thought that this worked at the time I put in this setting (March
31, 2002), but I may have been hallucinating...? In any case, it
doesn't work now.

Does anyone know what _would_ work? Or what other setting might
affect this?

Thanx!


- Steinar