doveadm backup : Warning: Deleting mailbox GUID= is missing locally

Hi,

As per the docs (https://wiki.dovecot.org/Tools/Doveadm/Sync) I'm presently running doveadm backup multiple times with a view to eventual server migration.

I am seeing messages such as this: Warning: Deleting mailbox 'Junk': UID=1826 GUID= is missing locally

Is it anything to worry about ? If so, how should I be dealing with it.

I also have a further question. It is not clear from the docs what the role of the "-R" flag is in relation to "doveadm backup" ? Surely by definition backup = remote -> local ?

Thanks !

Laura