Unsolicited email, often sent to millions of recipients at a time.

"Spammers" harvest recipient addresses from Usenet postings and web pages, obtain them from databases, or simply guess them by using common names and domains.

Sending spam violates the Acceptable Use Policy (AUP) of most ISPs, and can lead to the termination of the sender’s account. Many jurisdictions now consider spamming a crime, such as the US, which regulates via the CAN-SPAM Act of 2003.