[Dovecot] MBOX to MAILDIR conversion

Thinking about going from mbox to maildir. Started with mbox way back when but thinking about making the conversion. The main reason is that I use rsync for backups and when these huge mailboxes are touched I have to copy the whole thing. With maildir I only copy the files that change.

So - my questions is - what's the easiest way to make this happan. I assume there are conversion utilities. I'm using Exim as an MTA.

Also - using Ext3 for the file system on a Raid 10 array. Backup server will run Ext3 Raid 1. Is the number of files in one directory going to be a problem?

And - any tip/tricks would be appreciated. Things to look out for?

Still in planning stage.

Thanks in Advance.