@tristan957 @protonmail from a privacy point of view, Fast Mail is a bad option. They are under Australian legislation, where even IF they would provide #e2ee and #zeroaccess to your data, they would still be required by law to give law enforcement access to your data unencrypted.
https://www.wired.com/story/australia-encryption-law-global-impact/
If #privacy is a concern to you, then FastMail is not a good alternative.
mailbox.org would be a more viable alternative, but they do not provide E2EE calendars. Tutanota and EteSync are the alternatives I'm aware of providing the same. Only EteSync has a CalDAV/CardDAV bridge and native Android integration.