E-mail spam typically involves sending unsollicited e-mails in bulk-amounts. These e-mails mostly exist of advertisements sometimes combinated with phishing techniques to trick the receiver into visiting some website and preferrably making a purchase. Originally these kinds of e-mails were about selling medication like viagra, unproven methods against impotence, porn and more subjects on the "dark-side" of society, but the main character is that it comes from sources that do not have requests to send these e-mails and who are sending large amounts of these messages mostly based on harvested lists of working e-mail adresses. It can also use a technique of sending messages to unknown e-mail adresses and adding an "unsubscribe-link" at the bottom which isn't really for unsubscribing but actually for conformation that the "guessed" e-mail adress is a working one.
