If you use a hosted service, then unless it is specifically set up to prevent it (as with tarsnap for backups, which requires key management on the end-user's p

If you use a hosted service, then unless it is specifically set up to prevent it (as with tarsnap for backups, which requires key management on the end-user's part), the people hosting it will have access to your data. If that's a major issue, then your only recourse is to host it yourself. Running a mail server isn't terribly hard, but it does mean that when the server dies you're on the hook for fixing it. If you're not a sysadmin, then the pragmatic choice is probably to accept that Google doesn't care about the details of your email and will only be spying on you in aggregate to determine what adverts to display.