[oib]

You can't do end to end encryption if the receiver doesn't know how to deal with encryption stuff.

The second best thing to do is to use a e-mail provider that encrypts your e-mail using asymmetric key the moment they receive your mail. It protects you against search warrants but not active eavesdropping of your mail. And if the receiver's mail provider is being eavesdropped or receives a search warrants then there is noting you can do.