[exim] MBX format - converting to it

OK - fighting various problems - mostly with Outlook - and I think I
need to convery from the default dumb unix format to MBX format.

I'm married to UW IMAP and can't change without extreme pain involved.
Yes maildir is better - but not an option at the moment. As I understand
it - MBX will give me full file sharing and that - hopefully will fix
several problems I'm having.

So - I need to convert about 1000 folders to MBX - what do I use to do that?