PYPEM is an email client that allows your email to be left in the public domain yet remain perfectly secure. It uses RSA cryptography keys to secure your emails, you can leave private messages on public forums, send them in insecure emails or insecure communication programs and be certain that only the recipient will be able to read them.

The system uses RSA signing which guarantees that the email is coming from the source that claims to have sent the email, same applies to the emails you send, the receiver is guaranteed that the message did in fact come from you.
Due to the way the encryption works, there is no need for secure servers or secure communication networks.

Nobody, not even the server can read your messages.

http://cybercritics-critic.blogspot.co.za/2017/12/pypem-public-yet-private-email.html