I mean it says you can self host it yourself... and its on github and opensource, and if it's using openai api, you can always use a self hosted api that's compatible with openai api to run mistral or llama to run it all locally.
Yes, you're right, but I don't know if it's possible to replace the tinybird component with anything local, perhaps there's a convenient alternative I'm not aware of (I'd never heard of tinybird before seeing it in the README's list of external services). Either way, the documentation doesn't have a lot of information about a local-only use case, so I can only imagine it would be inconvenient. If they add support for self hosted mail sources in the future, it may still be worth trying though.
Yes, atm it relies on Tinybird. But the level of trust you need for that is different. And the data in Tinybird is encrypted so even if you don't trust them to run a Clickhouse database, if you set an encryption key they won't be able to do much with your data.
We are planning to support a version that doesn't rely on Tinybird at all but stores all data in your browser using indexeddb.