Account filtering function for filter email for your domain base (account) base level. It means, all of your email user will be applied with this filter. To proceed, follow the below step :
Step 1 :
Login to your cPanel and look for "Account Level Filtering" under Mail option.
Step 2 :
Create a new filter.
Step 3 :
Fill in you filter accordingly. For below example, all body of email contains word "Viagra" will be discarded. Save your filter to applied changes.