Please check the following to see if it works:
1- make a Dictionary containing your 100 words, where weight of each word is set to 1 and the threshold set to 3.
2- make a Tagging Rule in which 1st step you choose Application Definition as Email Client Applications (if I were you I would add Explorer as well for the attached files) and in step 5 you choose your Dictionary of 100 words, and in step 7 give it a proper Tag.
3- in Protection Rules make a new Email Protection Rule in which you go to step 2 and choose your tag and in step 9 choose yr desired action.
It should work!