OK, thank you for the informations. The following is the case: Yahoo is already filtering out many SPAM-emails for you. However, they can´t filter all SPAM emails, it´s simply impossible. But, you can tell Yahoo if a message is SPAM or not. Apart from that this will move that email out of your inbox into your SPAM folder, Yahoo´s SPAM-filter will become more "intelligent" with each mail you report as SPAM to them. Please have a read here how exactly you do that in your Yahoo mail account:
Ultimately, you will never be able to filter all SPAM emails out, but by marking SPAM emails as SPAM in your Yahoo account, you will be able to at least reduce them a lot! Personally I am a PC expert since 17 years, have all kind of SPAM-filters installed and train them every day, yet still about 4 to 5 SPAM emails make it through to my "legal" inbox each and every day. It´s one of those things which we hate the internet for and which we never can prevent 100%. It´s what we have to "withstand" on the internet if we want to use all it´s benefits on the other side.
Please let me know if I can provide you with further informations by just replying to this message again. In case I answered your question to your satisfaction, I would appreciate if you could rate me with 3 to 5 stars, because I am independent expert and only get paid by JustAnswer (they will send me a few % of your payment) if you give me a 3 to 5 stars rating.
Thank you very much and best (SPAM-free) regards,