[exim] high availability mailboxes... ?

Hi guys,

This may be a little out of scope for this mailing list, but I have a
quick question regarding high availability.

I currently have a requirement to provide high availability mailboxes
(via IMAP) to a few hundred mailboxes. The obvious solution here would
be to use something like NFS to store the mailbox data and access it
across two servers.

However, shared disk isn't an option in my current environment, so I was
hoping some of the guru's here had some suggestions as to how I could
have a mail replicate across multiple servers (like powermail can do,
but supporting IMAP), taking into account that both IMAP servers would
actively be servicing clients (ie, active-active).

Any suggestions as to how this could be done?

Thanks in advance,
Marc