The state will be 'opened' after first time email is opened. Each
successive open triggered warning, because state was already 'opened'
and thus did not match domain state in (sent, delivered).
Forward-port #d9ad3464
- Any model inheriting from mail.thread will have a filter available to
obtain records with errors in their messages trackings.
- The messages can be marked as done to avoid false positives when the
issues are solved.
