I don't have time right now to explain myself better, it's the minimalism and some features like snoozing emails, quickly marking them as done/low-priority and similar things, which is definitely not something that is connected to Google technology.

> It sounds like you want a client that is tightly coupled with Gmail's features

I actually don't like Gmail that much.

> you're not going to get that with a non-Google client.

Google Inbox used be called Sparrow (https://en.wikipedia.org/wiki/Sparrow_(email_client)), which was a regular app that Google acquired. I used it since the beginning. It was a new paradigm back in 2011, which is now the standard in modern clients.

Thunderbird needs to rethink their approach. They need less buttons and more focus on important features over other ones you barely use. In Thunderbird, everything is given the same importance in the UI. There's a toolbar with 100 buttons of the same size: "Write, Chat, Reply, Reply all, Archive, Address book, Get email, Tag, Quick filter". Why is "Chat" the same size as "Write", and right next to it like it's the most common feature in an email client? Why is "Address book" even there, given the same importance as "Write"? Who browses his address book randomly? Why can't they just show suggestions when I'm in the compose window and I type the first few letters of the person's name or email?

I could go on forever.