When you enable SpamFilters from cPanel, this will mark all suspicious emails as spam and will add the prefix *** SPAM *** to the message title.
You can make spam emails delivered to your SPAM folder instead of reaching your Inbox by creating a global filter from cPanel > Global Email Filters
- Click Create A New Filter button
- Give the Filter a name by typing the name in Filter Name field.
- From Rules list, select Spam Bar, then select Contains from the next list and type +++++ in the text field (+++++ means spam score is 5 or more)
- From Actions, select "Deliver to Folder" and click Browse button and select Spam folder
- Click on Create button
From now on, all spam emails will be delivered to the Spam folder, and this global filter is applied to existing and new email accounts that you may create in the future.
UPDATE:
SPAM box is now enabled by default.