His page (http) -> MITM -> page you get with another public key You write him something -> he doesn't read. You write him -> emails is intercepted -> he doesn

His page (http) -> MITM -> page you get with another public key You write him something -> he doesn't read. You write him -> emails is intercepted -> he doesn't read it but who intercepted the email reads. So his computer is never compromised. But his email server (some provider) is.