Email just once about comments until we visit the site
You know how Facebook and other sites will send you an email about a comment for a thread you've subscribed to, but they don't send any more emails about activity on that thread until you visit it? I think Letterboxd should do the same thing. I'm afraid to not check my mail for more than 2 hours for fear I will have thousands of emails from Letterboxd.
We did take this approach initially, but then we decided to include the comment text in the email, which removed the need to return to the site at all in order to keep reading the thread. Which meant we had to always send emails.