Excellent contribution, devil! I like the use of ssh and I'm sure other users will as well. A couple feedback points, taken from when I did my own shell script backup (you may have seen it
here):
- You might want to do a two-step rsync--once before stopping Zimbra services and a second time afterwards. This allows for a much faster sync while Zimbra services are stopped, and consequently has the mail service down for a much shorter period of time.
- I use
Code:
rsync -avHK --delete
as my rsync command options (see rsync man page):
-a --archive mode; equals -rlptgoD (no -H,-A,-X)
-v --verbose mode, useful while debugging
-H --preserve hard links
-K --keep-dirlinks, treat symlinked dir on receiver as dir
and --delete to keep the backup file from growing ever-larger as deleted emails otherwise will stay in your backup forever. I didn't realize this till my backup file had grown from 2gb to 8gb with little change in mailstore size. . .you don't wanna go there! 
You may wish to consider similar modifications.