"So I’ve given you my email address. I’ve given you the permission to contact me directly, via the medium I check more than anything (nasty habit, I know.) And this is how you repay me?"

Hear, hear. We've been preaching the same at Mailgun. A lot of companies pay good money for affiliate lists, scrape web sites; basically do whatever it takes to get emails for marketing/spam. Yet, here are companies with permission to engage their users through email and they totally whiff. EVERY email you send should be considered an opportunity to increase engagement with your users. Tell them them that they can respond with questions, comments, whatever. Grubwithus does a good job of this. They specifically say in the body of the emails that you can provide feedback just by replying.

Email should be considered another interface into your application.