Activate Posteo crypto mail storage for your account: This function encrypts your entire email data at the press of a button, including all content and metadata. The encryption is comprehensive; it encompasses your existing email archive, all newly-arriving emails and your notes.

To be honest, this sounds like gobbledyremoved aimed at duping people who don’t understand cryptography. The problem with encrypted email is first of all that it only works if both sender and receiver agree to do it. You cannot use your posteo account to send an encrypted email to other email users, because they wouldn’t know how to decrypt it! Likewise, incoming emails can only be end-to-end encrypted by the sender; if the sender sends them in plain text (which all but one in a million email users will), the server receives them in plain text. Even if the server “encrypts” them for storage, the plain text is still available to the server.