I’ve just moved to Thunderbird. I was never keen on the old design and found it rather clunky but the new UI I find much better.
I was using Mailspring but it has recently just refused to work on my device and I never even got a response on the community forums so I’ve just given up on it.
Willing to give this a go. My go-to for getting non-repo debs automatically has been deb-get which works well but seems susceptible to issues when changes in the software it lists causes it to break and whilst the fix itself is usually made pretty quickly, it seems to go long periods of time between PR merges and releases (which includes adding new software). If this is a viable replacement for it then i’d love to start using it.