You could have a separate computer that is never connected to the Internet to compose your mail. Encrypt it with a program you write yourself to avoid the legally required back door. Use a thumb drive to transfer the result to the Internet computer where it can be emailed. The recipients move the encrypted email to a similar no-Internet computer to decrypt. Even this isn't foolproof, but I say good enough.

Though all this might motivate a pre-dawn SWAT raid on your home. Just what are you trying to hide?

Or you could use traditional paper mail.