Outlook Rules work inconsistantly

I am being bombarded with spam. I have set up some Rules to try to filter out certain e-mail messages that contain certain words. For example, I get about 30 messages a day with the word “re-finance” or “mortgage” in either the Subject or the bodyof the message. I set up a rule to delete any message that has either of these words in either the subject or the body. Sometimes the rule works, and other times it doesn’t. It doesn’t matter if I have the Rule running while I have Outlook open or if I choose the “Run Now” option.
Does anyone know why the Rules work so inconsistly?
Thanks.