[Dovecot] rdiff-backup of Maildir?

What's the best way to do long-term backups of the Maildir format these days? Traditionally we've just done a rdiff-backup or pointed Bacula at the Maildir. Both give us the option to reset a particular mailbox back to a previous day (any day within the last N months).

Do we just need to snapshot the LVM volume that holds all the Maildir boxes, or is there some additional commands that we should run before doing the LVM snapshot?