If you want to make sure that no one reads your email messages, you need to encrypt your email messages using a digital signature certificate that’s available for free from Comodo.
Watch this video that shows how to encrypt email messages using digital certificates in Outlook 2007 and Outlook 2003. Before you can send encrypted messages, the recipient of the message needs to have a copy of your security certificate and you need a copy of theirs.
Related: Is Anyone Reading My email ?