SafeGmail
Send private e-mails through Gmail.
... it. You should be able to see the extra buttons in the Compose Windows in Gmail.
3. Write a normal e-mail, click 'Encrypt?' Checkbox, then write Question and Secret Answer.
4. Click Encrypt + Send button.
5.Reader should click on the link, answer the question, then COPY & PASTE only the encrypted message in the textbox.
Visual instructions in project webpage.