Backing up the open-source edition of Zimbra mail

Background:

We run the open-source edition of Zimbra mail (5, not 6 yet) and while it's not something that we want to encourage (prevention is better than a cure), we currently have no way of backing up (or restoring) mail in the system. The Network (paid) Edition has automated
backups; various user-contributed solutions exist for the open source edition.

My question in two parts:

1. Does anyone have experience performing backups on Zimbra OSE? I'm particularly interested in snapshot backups over ssh/rsync (we use dirvish for filesystem backups), and we don't use LVM (/opt/zimbra/store/ is it's own partition, the server is Ubuntu on ESXi).
2. If backup/restore on a live system is "too hard", I'm happy to settle for backing up only specific shared accounts that are never logged into directly (and hence I have the password for) over IMAP. I'd be interested in recommendations for a command-line email client that
   1. can be automated to retrieve messages & folders (e.g. given command line parameters / config file, will log in to account, fetch new email, quit)
   2. stores email in the maildir format, which is nicer to backup than mbox

I'm leaning towards the second with something like isync, since the mail system has over 100GB of messages at present.