Are the emails you send normally private and confidential? If so then you won`t want others reading them. The most practical solution is to have a program like Easy Email Encryption Lite, which lets you encrypt their content so that only the receiver can read them.
Easy Email Encryption Lite works with any email program (although it has been specifically designed for Outlook Express). Obviously the receiver of the email has to also have the program so they can de-encrypt it using the password that both know.
Easy Email Encryption Lite is really easy and intuitive to use, even for novices and inexperts.