There are terrific tools (like PGP and GPG) for encrypting your mail. If somebody along the way looks at the mail they can't understand it. But they do know you are sending encrypted mail to your pal.
The answer: encode your message into something innocent looking.
Your messages will be safe and nobody will know they're encrypted!
There is tons of spam flying around the Internet. Most people can't delete it fast enough. It's virtually invisible. This site gives you access to a program that will encrypt a short message into spam. Basically, the sentences it outputs vary depending on the message you are encoding. Real spam is so stupidly written it's sometimes hard to tell the machine written spam from the genuine article.