While I can understand the reason you want this, it's probably an isolated instance even for you - do you really want to get constant notifications for low-priority email messages (or spam) until you attend to them?
I'd guess most people would find this so annoying that they'd disable it, and start posting here about how useless/annoying the setting is (and questioning Apple's sanity). And for those who have a tendency to play with their settings without really thinking about what they're doing (like adults who enable Content & Privacy Restrictions when children never touch their phones/iPads).... forget about it!
Since this is a single email message, what I'd suggest is to set a separate Reminder or Alarm. In other words, treat it like an appointment, rather than a piece of email.