You are indeed quite rude, but I'll give you an answer.

The selling point is that it's IMAP primitive, as the blog post mentions.

Thunderbird is nice, but it's not cross-platform. Superhuman and Notion Mail are nice, but they only support Google and Outlook.

Apple Mail is truly awful.

There's a gap in the market, and as I said we're building it for ourselves.

Yes, because as a business you shouldn’t have a sales pitch ready for people when they ask you why they should spend money on your product.

It’s the first thing you do if you are trying to make a product that you plan to monetize is ask - who is the ideal user and how will we market it. If it’s just a hobby project to learn a new to you technology, that’s fine or if you just wanted to scratch an itch.