From AptivateOER

Security and privacy

Generally, the email you send and receive is private to you and those you are emailing. Everyone with an email account has a log in, providing their unique email address and password in order to read and send email. If you don't tell anyone your password, there shouldn't be anyone else reading your email.

However, emails cannot be viewed as entirely secure means of communication. It is possible for people with the technical understanding to intercept emails as they travel through the internet from your email account to the recipient's.

These people are mostly interested in trying to find any financial details, or other personal details that can be used to their benefit.

You can look view this as an analogy with the postal system. You wouldn't write sensitive information on the back of a postcard because anyone could read it on the way.

This is not to over-worry you and in all likelihood, most of the emails you send are not being read by anyone except the person you are sending it to. But nor can emails be viewed as completely private all the time, so you need to ensure you keep very sensitive or important information that someone else could exploit, out of emails.