Auto-unsubscribe option per category

Issue Summary

I think there needs to be a category based option to unsubscribe users when they received all the emails in this particular category. This should be optional in case some categories get new emails and others have limited number of emails that don't update.

For example I have 3 follow up emails with my prospects - after they received their 3 emails - I don't want to keep them still subscribed to the same follow up category.

Hope this makes sense.