[upofadown]

You can't really just shop for privacy. If it is important you really have to do the encryption using software under your control on the end devices. For email this would involve local email clients supporting OpenPGP or S/MIME.

For a closed group like a business you can simplify things by having a self hosted email server kept in a secure location. Less secure than end to end encrypted email, but then, few things are as secure as E2EE email. It's hard to beat a medium where the encryption can be done completely offline.