Over at SuperUser meta, they reckoned that my question belongs here.
Personally, I am not so sure, but thought that I would ask.
To quote:
My web host company handles my email & they run it through Apache Spam Assasin.
Using CPanel, I only see options to black/white-list domains, but I would like to mark as spam based on certain words in the email subject.
Is it on-topic to ask on this site how to do so?