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.
Out of curiosity rather than necessity, are there any activitypub based messaging apps (i.e matrix/discord-like)?
One not listed is Ibis (https://ibis.wiki/) which hasn't had much traction. Honestly unsure of how useful it is as a direct wikipedia replacement but i can see it as a cool idea for a bunch of related communities that would otherwise be on separate wikis.