Error during Dovecot control files backup

Good evening to all,

During a check in the backup log files, I saw the following error:

for every email user, but the backup does not fail! I realized that on my server, dovecot user control files, are stored in directory like

/var/lib/dovecot-virtualmin/control/user@domain.com

so i think that the backup script do not find the directory because the user format is different...

Where can I set the right user format?

Any suggestion? :)

Thank'you so much for any help and sorry for my poor english ;)