E-mail spam slowly but exponentially grew for several decades to several billion messages a day. Spam has frustrated, confused, and annoyed e-mail users. Laws against spam have been sporadically implemented, with some being opt-out and others requiring opt in e-mail. The total volume of spam (over 100 billion emails per day as of April 2008) has leveled off slightly in recent years, and is no longer growing exponentially. The amount received by most e-mail users has decreased, mostly because of better filtering. About 80% of all spam is sent by fewer than 200 spammers. Botnets, networks of virus-infected computers, are used to send about 80% of spam. The cost of spam is borne mostly by the recipient, so it is a form of postage due advertising.

E-mail addresses are collected from chatrooms, websites, newsgroups, and viruses which harvest users' address books, and are sold to other spammers. Much of spam is sent to invalid e-mail addresses. ISPs have attempted to recover the cost of spam through lawsuits against spammers, although they have been mostly unsuccessful in collecting damages despite winning in court.

Overview

(ToS/AUP) of internet service providers (ISPs) and peer pressure. Even with a thousand users junk e-mail for advertising is not tenable, and with a million users it is not only impractical, but also expensive. It is estimated that spam cost businesses on the order of $100 billion in 2007. As the scale of the spam problem has grown, ISPs and the public have turned to government for relief from spam, which has failed to materialize.

Types of spam

Spam has several definitions, varying by the source.

• Unsolicited bulk e-mail (UBE)—unsolicited e-mail, sent in large quantities.
• Unsolicited commercial e-mail (UCE)—this more restrictive definition is used by regulators whose mandate is to regulate commerce, such as the U.S. Federal Trade Commission.
• Any email message that is fraudulent.fact: date=July 2008
• Any email message where the sender's identity is forged, or messages sent though unprotected SMTP servers, unauthorized proxies, or botnets (see Theft of service below).fact: date=July 2008

Spamvertised sites

Many spam e-mails contain URLs to a website or websites. According to a Commtouch report in June 2004, "only five countries are hosting 99.68% of the global spammer websites", of which the foremost is China, hosting 73.58% of all web sites referred to within spam.

Most common products advertised

According to information compiled by Spam-Filter-Review.com, E-mail spam for 2006 can be broken down as follows.