There is encryption at rest (storage encryption), transport encryption and end-to-end encryption. E.g. Posteo has transport encryption and optional storage encryption. With activated storage encryption, Posteo cannot read your mail because the encryption key on their server is only usable with your password (which they do not store). Proton Bridge adds end-to-end encryption to Protonmail
As someone else pointed out, maybe you’re thinking of POP instead of IMAP? I basically have all my mails on the host’s servers (including folders) and just synchronize using my different clients
Sorry, I kind of forgot about lemmy or a few days. In Thunderbird, I create a new dedicated folder, use Tools --> Message Filters. I then can add the desired filter (something like must cotain at least ‘host.tld’ in sender) and make it move all filtered mails into the previously created folder. I just checked, it works (you can also specify when that filter should be executed (e.g. when getting new mails or every 10 minutes) and the folder with the filtered mails also shows up in FairMail on Android. Better description: …mozilla.org/…/organize-your-messages-using-filte…
Do you actually feel it? I don’t feel it at all. Just at some point I am like “oh fuck, I didn’t listen to what they were saying”. And I cannot even remember what I was thinking