Log into into your cPanel account.
Choose the Spam Assassin link under the Mail section.
Enable Spam Assassin.
All your junk email will be delivered with the word ...SPAM... in the header.
Set up a rule in your email client to put all these emails marked with SPAM into a junk folder.
After testing this for a week if you are happy with the result go back into cPanel and also choose "Auto Delete SPAM"
This will then delete all SPAM at the server so it will not be downloaded onto your computer.
We also have a business class solution to protect your business from SPAM. Read more here