A number of factors can cause[url=https://www.emailtechnicalsupport.us/blog/yahoo-spam-filter-not-workin... spam filter not working Yahoo Mail Spam Filter Not Working[/url] error. They are listed below.
1- The inbox will receive all messages with an empty character if you construct a filter without any rules (i.e., an empty filter). If this filter is applied on top of other filters, it will nullify their rules and send all emails to the inbox.
2- All the rules are applied via a filter. The filter won't function as you want it to if the email doesn't adhere to one of the rules.