You are reading this article because you are using Non SSL settings in your email software.
Bottom line is: If you are not using secure connections in your email software, then you should be prepared to have your email login details compromised.
Imagine it like this: If you are in a room full of people and you want to send a message to someone across the other side of the room, you write your message on a piece of paper and hand it to someone. That person hands it to someone else and so on until it gets to the intended recipient. However, whilst its being passed across the room, becasue its written on a plain piece of paper, anyone can easily read it as its not hidden. Email is exactly of the same.
When you connect to the internet with your email software and you are not using a secure connection such as SSL, you are sending data in "plain text", then anyone with some small amount of skill can pull your transmission from the internet and read it. When they do this, they also have access to your login username and password and then they can then use those details to send out spam on your behalf.
It can also lead to more serious abuse. Once someone has access to your email account, they can possibly steal banking data and other sensitive personal data leading to identity theft.
We STRONGLY ENCOURAGE all our clients to use SSL connections wherever they can.