It's hard to completely stop spam e-mail but you can filter it, discard it, deliver it to selected folder, etc.
How to Create Account Level/Global Email Filter?
1. Log into your cpanel account.
2. In the "Email" section, click on "Global Email Filters" Icon.
3. "Create a New Filter" Enter a name for the filter in the Filter Name text box.
5. In the rules of the filter you can filter e-mail by many options, and should you want to deal with e-mail which contains a word like "Lottery" or other words, then select "Contains" under the "Rules" list, select "Body" from the 2nd drop down list.
6. Under "Actions" list select "Discard Message".
7. "Create".