[exim] dealing with LMTP errors

I am getting non-spam emails that fail delivery over LMTP to Cyrus IMAP.
Most likely the cause is lines that are too long (though it could also
be embedded NULLs).

I would appreciate suggestions about how to handle this, assuming I'm
stuck with Cyrus's behavior.*

Ideally some kind of filter could clean up the message; I haven't turned
up one on the net and am a little concerned about trashing attachments
if I just do something naive.

A cruder approach would be to reset the the enveloper sender to a
special address on my system, and have mail to that address delivered to
a regular mailbox in my home directory. It would also be good to have a
notification sent to me so I know this is going on; I guess I could do
that with a second router for the special bounce address that used a
pipe to send the alert.

Any thoughts?

Thanks.
Ross Boylan

(*) Some discussion on the net suggests that a change existed or was
forthcoming, but I don't see it in the cyrus changelogs, even for 2.4.