Go to your Mailinblack Protect interface, then to the Settings menu and click on General settings and "Email filtering by keywords" section to unfold the settings.
How to filter your emails by keywords?
Click on "Add a filter" to add a new parameter.
Configure your filter by providing its name and the regular expression to filter
Select the category for your filter. Here, you will choose if the emails matching the configured regular expression will be categorized as infected, Spam, banned, or valid
Here is a website that will help you configure your regular expression: https://regex101.com/
If you enable this option, here is the order of verification for your email through Mailinblack:
Anti-virus filtering
Keyword filtering
RBL check
SPF check
Check of the authorized and banned senders list
Authentication request.