Fastmail. They are cheap enough, and featureful. They allow you to use your own domain, and support IMAP and calendars. I would like to say protonmail, which i

Fastmail. They are cheap enough, and featureful. They allow you to use your own domain, and support IMAP and calendars. I would like to say protonmail, which is cheaper and has a more secure email setup (which involves encrypting incoming emails as they come in) but because of this it doesn't support IMAP integration without an extra decryption daemon. Ultimately this extra security is useless anyways because the email protocol is weak to MITM (see lavabit situation).