That's not a great solution. list_subscriptions() will return an empty array to syncroton, which will force re-synchronization. Unfortunately there are more than one IMAP command on the way that can go wrong, and maybe it's not only IMAP. But maybe we should use rcube_imap::get_error_code(). Its result will be non-empty if the last IMAP command returned an error. However, we don't know if that was an error or just an empty/invalid result. There's a few IFs here.