[Exim] Sieve filters and vacation msgs

Hello all,

We are building a new mail platform and have chosen Courier/Maildir for our mail
store, Horde/IMP for our webmail and of course Exim 4.34 as our MTA. We have
altered Horde/IMP so that it FTP's a sieve filter script up to the mail store
and we have got Exim using this sieve filter to forward, whitelist, blacklist,
fileinto folder etc.

The only missing pieces from what I can see now are the 'reject' and 'vacation'
parts. Now, I know 'reject' is not supported as Exim doesn't support MDN's -
I'm guessing this will also apply to the Sieve "vacation" extension too? I
don't mind removing the 'reject' option - but I'd love to get vacation message
processing going.

If this cannot be done via Sieve then can anybody suggest the best way of
handling vacation messages - I'm prepared to do a bit of hacking to get it to
work - but I need some advice on the best way to do this with Exim.

Cheers,
Ray