Most spam blockers work by inclusion. That is, if you mark an email from the ABC Company as spam, anything they send to you from then on automatically goes into your spam folder.
But, you may have noticed, that does not seem to work anymore. Spammers now send out their trash under a different name each time but with the same sending name, such as the ABC Company. Anyone can use anything as a sending name. You see the ABC Company as the sender over and over again, but your spam filter thinks it is from someone new each time and leaves it alone. You can see the real name in Yahoo! by hovering your cursor over the name that appears on your email inbox, and the real name pops up. It is totally different from the sending name you see and often seems to be a random selection from the dictionary. With AOL, you need to right-click on the name, then “View Message Source.” All browsers I know of provide some method to show the real name of the sender.
The idea of a sending name started out with good intentions. Your real email name, your email address, may be “fdfghj@Browser.com,” but receivers will see it as something like “Greetings from Ed and Betty,” a nice touch that they are sure to recognize.
Your alternative is to specify spam by exclusion—anything not matching a name in your contact list is spam, but then you risk missing an email from an old friend who is writing to you for the first time.
You can’t win; the spammers do.