Hmmm. Please can you provide some details as to what program/s you're using to send/recieve mail and how you connect to your ISP? There's more than one way to achieve this, all of it dependent on type of program, operating system, method of connection etc.
I use Linux 6.2 and have no problem blocking spam on the domain this runs on, but I suspect you're on Windows in one form or another.... It can still be done, but more info please.