> It seems like people ... just don't even look in their inboxes for legitimate, personal correspondence anymore

I disagree with that - in my experience sending persona correspondence to my friends/family are generally received and read.

It does seem like people really want the "like (with an emoji)" funcitonality of the rest of the web in email ... Gmail and Outlook are building it in, but unless you're in their walled gardens it does not work great (i.e. email reply: "X has ed your message")