We do not want tickets re-opened. It would be nice if anyone posting a comment via email to a closed ticket receive an automatic message that their comment will not be seen and to open a new ticket via the Portal.
You can do that with an automation rule.
I know we can send notification of an ad-hoc email, but how can you target the poster of the comment? It may not be the original requestor. There is no generic "Commentor" that I could find.