[exim] Blank Message-ID:

Is there any way to strip out the Message-ID: header from incoming
emails if it is empty?

I've found that email from a Lotus Notes server sent to my system
(exim+cyrus) gets rejected.

That's because the Message-ID: header is blank (rfc2822 not
withstanding), and so when exim attempts to deliver this to cyrus, cyrus
rejects it with "554 5.6.0 Message contains invalid header".

I've added this next line to my exim.conf file:

headers_remove = message-id

which means that everything works, but of course I no longer have the
Message-ID. Is there any way to make this conditional?

Thanks
Luke Diamand