Change backup to sync -1 to avoid doveadm failures
Change backup to sync -1 to avoid doveadm failures

Was:

dsync(ikr): Error: Mailbox INBOX sync: mailbox_delete failed: INBOX can't be deleted (0.000 + 0.000 secs).
dsync(lesya): Error: Mailbox INBOX sync: mailbox_delete failed: INBOX can't be deleted (0.000 + 0.000 secs).

ikr/ikr.su-server,ikr/ikr.su-server