If you are running an outdated version of Outlook, then the Outlook Spam Filter Not Working issue can occur. Alternatively, the spam filter may not be able to detect and block spam if the spam filter settings have been set incorrectly, messages.
If you have an outdated antivirus program installed on your machine, it may not be able to detect and block the most recent spam messages. An ISP that has not configured its spam filters correctly may also cause the spam filter to not work properly.