You can't. we don't parse your E-mail to provide you with targeted ads, nor do we read E-mail contents.
However, it is 100% possible for use to read E-mail, and IMAP/SMTP doesn't provide user-side/client-side encryption,
so you're just going to have to take our word for it. Any encryption implementation would still technically allow use to read E-mail, too.
This was true for Lavabit as well -- while your E-mail was stored encrypted (only if you were a paid member, which most people forget),
E-mail could still technically be intercepted while being received / sent (SMTP), or while being read by your mail client (IMAP).
For privacy, We would recommend encrypting your E-mails using PGP using a mail client add-on like Enigmail. Our Web Mail | CgAn Panel-Mail provides encrypting your E-mails using PGP.
How to use PGP: