Yahoo and Hotmail both have filters to their free e-mail service entitled Bulk Mail . Some filters can be downloaded from the Internet. Spam exists because somewhere, someplace out there, there are millions of people who respond to it. This site analyzes the spam mail and finds the true address. Then they report the spam to the owner of the server.
Unwanted email does the same thing - it is louder than all other conversation on the internet.
SPAM is a registered trademark of Hormel Foods Corporation.