Using separate notification sounds for high-priority emails

I typically receive a few hundred emails a day and don't use a notification sound - it would be ringing off the hook if it chimed for every email that arrived on my phone. I want to be able to identify a few contacts as high priority or high importance and have a separate notification sound when I receive emails from them. I can already set a separate ringtone for specific contacts, but I can't change the email notification sound in the same manner.

This is probably a feature request. I don't believe that this functionality exists currently, but I think it's especially important for business users.