[exim] Vacation messages

Hi,

We make extensive use of Exim filters for vacation messages. Recently our
local county council has started using prvs return-paths, and testing for
them.

This has broken our vacation messages, since the "mail" filter command
sends email with a null sender, but uses the "reply-to" or "from" headers
for the recipient.

I *could* specify "to $sender_address" in the filters (they're generated by
a web tool that we provide), but that would mean the replies would have
addreses like prvs=foo.bar=5217c133d@???… in the To: header.

Is there a way that I can use an envelope recipient address that's
different from the address in the To: header?

Are there any other draw-backs to using $sender_address as the recipient
for a vacation message?

--
Ian Eiloart
IT Services, University of Sussex