Maybe everyone is waiting for someone smarter than themselves to answer this.. :-)
Maybe... but at the same time, there's a risk of me abandoning Dsync for rsync or something else that I know I could have implemented by now with far less frustration ! However I'm keen to learn how to utilise the power within Dsync.... ;-)
So.. hoping I read and understood your email correctly ...
Hoping that email wasn't too confusing ;-(
The first thing you tried failed because only root can change permissions, except for using the setuid bit which is probably not what you want here. The second might have failed because of:
userdb { args = username_format=%u /etc/dovecot/users driver = passwd-file }
dsync is using userdb and not authdb because it's not checking a password here. Can it be that its-virtmail doesn't have permission to read /etc/dovecot/users ?
hmmm ... its chmod 640 root:dovecot on the primary server and the same on the backup box. Do I need to mess around with permissions on both or just the backup box ?
I was under the impression that Dsync was just a more modern version of a doveadm tool that went by a similar name and hence assumed it would use dovecot permissions.
But then again, who knows... I was getting very confused at the end of a long day trying to make it work !