Regular email is unsuitable for serious messaging applications. It can easily be monitored while it travels through the Internet and it is even easier to monitor when stored on mail servers.
Encryption enables the use of email for private and protected communication with clients, business associates, family and friends.
When looking for a secure email solution, look for end-to-end encryption that secures email transport and storage. Avoid so called "secure email" solution that only encrypts transport (SSL) and leaves email content in plain text while stored on the servers or computers.