do you mean SPAM or do you want to block senders?
You can't block senders yet in the Win 10 mail app: http://answers.microsoft.com/en-us/windows/forum/windows_10-security/block-email-senders-in-windows-10/f1f9bb67-2649-4554-8c4d-4d93a60307e4
OMG, you can't block SPAM either: http://www.geekstogo.com/forum/topic/360286-any-way-to-block-spam-on-windows-10-mail/
why release an email app that doesn't block either of those??
I guess I would have noticed this if I didn't still use Gmail web client. I can't think of an alternative, Windows Live Mail still works on win 10 but no guarantees that will continue