mnemonicj has it spot-on. In your situation, you are limited to whatever spam-blocking your ISP has available. Different mail providers have different degrees of spam-prevention, and this is often a factor when choosing who to get your email through. It certainly was for me. If you don't want to change email addresses, there are some services that provide spam-filtering by means of forwarding, but they can be messy to set up.
Unfortunately with free email services, your options are limited. For many years now I've considered email to be something worth paying a little for in order to get a better product that's more-reliable, as email is important enough to me.
One advantage of having your own domain for email is it makes changing email providers, or routing through a forwarding service, very easy.