Proton is probably the slickest, most feature-rich and solid email service. They have a suite… Mail, VPN, Calendar, etc. I pay like $50 yearly for it, which gives a lot of extra settings. But even in the free account there is a “convert from Gmail” option that downloads all of your Gmail emails into your proton account. It’s the easiest way to degoogle. Plus, all proton-to-proton email is automatically PGP encrypted, even if you use custom domains. You can easily setup auto PGP for other external services that offer it too, so emails are seamlessly encrypted between them.
This short guide gets you up and running with Proton Mail if you are transferring your files from Gmail. You can seamlessly move the emails, attachments, calendars, and contacts you have stored in your Gmail account to Proton Mail and Proton Calendar