I've been building a Thunderbird extension that gives me the mail view I want.

So far it's mostly just configuring hotkeys to tag messages, and settings to hide or fold messages by tag, but I can trivially add functions to parse common messages, send things to my todo list, etc. It's great how easily programmable this is. I threw together a "summarize message with Gemma4 on Ollama", and it wasn't useful, but was a quick and easy experiment.

Thunderbird extensions are just Javascript using the Thunderbird API, and Claude knows the API, so it's a super-low barrier to get started on your own personal extension.