I've done my research just yesterday and decided upon mailbox.org. I fully switched over in less than 4 hours. It's hosted in Germany (GDPR regulations and rea

I've done my research just yesterday and decided upon mailbox.org. I fully switched over in less than 4 hours. It's hosted in Germany (GDPR regulations and reasonable privacy), supports custom domains, provides cloud storage and office suite and supports full inbox encryption with your own public key - the service provider allegedly can't even read your email after they encrypt it. To move your existing email from GMail, first remove large junk/spam/ads emails and then download everything with Thunderbird over IMAP, then slowly copy emails to mailbox.org folder. It also provides cloud storage (which I intend to use in addition to Syncthing) and cloud office suite.