Spam email is sent by purchasing or compiling lists of email addresses and using computerized methods of barraging the addresses with messages. Lists come from a variety of sources, including Internet chat rooms and news groups, where spammers use software to harvest email addresses.
Specialized search engines known as spambots search the web for addresses that can be added to spam lists. Some legitimate websites also sell lists of their customers to purveyors of spam email. Spammers often share their email lists with other spammers.
Spam is sent through companies that offer bulk emailing services. Some such companies send billions of spam emails each day and often work from countries outside the United States where unsolicited bulk emailing is legal. The CAN-SPAM Act of 2003 provides rules for sending commercial email within the United States.
The most effective way to stop spam is using a software filter. Some filters use particular words to determine which emails to delete before the recipient views them. Spammers often thwart simple filters with intentional misspellings of words commonly used in spam. Advanced filters use word frequency and patterns to try to identify spam.
The term "spam" comes from a 1970 sketch by the British comedy group Monty Python targeting the canned luncheon meat Spam. The sketch poked fun at the meat product as being everywhere, and the term was later applied to unwanted commercial email.