By default, the email service we provide you along with your hosting is outfitted with a well-tuned spam assassin system to detect incoming spam to your users' mailboxes. Any message detected as spam will have *** SPAM *** prepended to the subject. By default those messages will still arrive in your inbox, however.
We have a "spam box" option which will filter these messages out of your inbox, into a spam folder. To enable this for all of your mailboxes, log in to your control panel, click the Spam Assassin icon, and look for the button to enable the spam box.
Anything that is filtered out of your inbox, and into your spam box, will be automatically deleted when it is a week old. This gives you an opportunity to check your spam box to see what is being filtered.