I would like to do incremental backups of the users' maildir directories to a dedicated backup host (using "rsync -SHa" and rsnapshot).
dont use it.
use rsync -b option. It is MUCH MUCH BETTER.
i use it regularly.
Split your rsync session if you have huge amount of users or rsync would be taking enormous amount of RAM and have larger chance to fail.
Problem is: Dovecot bloats the incremental backup by changing the file names again and again.
I didn't observe that except when moving from "new" to "cur"
but --detect-renamed fixes it.
Is there some way to tell Dovecot to keep meta information separate from the file names?
it already do this.
exclude dovecot indexes from backup
PS. rsync backup is what i use regularly. Except none of my servers are purely mail server.