[exim] rewriting From header and envelope sender

Hello,
I would like your opinion on a possible envelope and headers
rewriting for authenticated outgoing messages in a way analogous to
VERP (I believe).

Story: when giving a contact address to an unknown recipient I always
(almost) use a return address with encoded the domain of the
recipient in the local part suffix, so that I can whitelist it (if
necessary) or even find out if the recipient does bad things with my
address*.
Unfortunately many MUA do not allow changing the envelope sender or
even the header From: if not doing some configuration steps (and
making an already long list longer...).
With an automated rewriting (not in the canonical meaning of address
rewriting in exim) I would instead just use a particular suffix (or
prefix) and exim would rewrite the address using the (only) recipient
domain. For example: sending an e-mail from foo-rewrite@???
to bar@??? would have the envelope sender and h_from rewritten
as mail foo-xxx.xxxxx@???.

To accomplish this I could presumably set an acl variable in the rcpt
acl with the rewritten address and then in the router change the
From: with headers_remove
and headers_add, and in the transport change the return_path.

Apart from the technicalities, do you think there are any major
drawbacks? I do not care about digital signatures as long as they are
not used with untrusted recipients.
Certainly a device like this would make much easier for most users
not to give away their real address too often.

Giuliano






*(Once I found virus coming from an address that I had used a couple
of weeks earlier with LG, in the face of any data protection act/
privacy laws).