We actually agree with you. There is fine line between sending emails that are an annoyance and emails that hold value.

Email is an extremely effective tool for both marketing to and communicating with your users. Our aim is to make event-based emails as targeted and personal as possible. If a user receives an email pertinent to their personal situation it's much less likely to be received as an annoyance or spam.

You need to respect the inbox but that doesn't mean you can't use it at all!

I find that personally I don't mind if I get some kind of initial email, as long as I'm able to opt out (easily) and they inform me of my ability to do so, just like the example from Buffer in the blog post.