All unsolicited bulk e-mail is spam with the following exceptions:
In essence, ISPA believes that consumers should only receive bulk mail that they have requested and/or consented to receive and/or which they would expect to receive as a result of an existing relationship.
Spam, or unsolicited bulk email, is the posting of emails to large volumes of addresses advertising a service or product which the recipient seldom wants. Unlike conventional junk mail where the sender pays the cost of postage, recipients of spam pay the transmission costs, either in the form of Internet access fees and/or telephone call charges.
An example of spam is an unsolicited email message from someone you dont know (or a forged address) inviting you to view pornography, purchase Viagra or enlarge your penis amongst other things.
Spam is one of the most significant threats to the Internet, accounting for around 60% of all email traffic. Spam costs consumers and ISPs lots of money in bandwidth charges. Despite the growing number of technological means for combating spam, the spammers somehow manage to stay one step ahead and the deluge shows little sign of abating.
Spammers get email addresses in a variety of manners:
One of the ways in which spammers check for valid addresses is by providing an apparently thoughtful Click here to remove yourself from this list with a URL pointing to a website. The user seeking to prevent further mails from the spammer clicks the link in a trusting fashion. However all they have done is verify that their email address is active, which results in additional spam being sent to them.
Another means is to insert a pixel image into the email which links to a web server. When you load the message in an HTML capable mail client, the mail client requests the pixel image from the configured web server. By accessing the image and downloading it, a line is added to the web server log file which can be used to verify an address which spam was sent to.
Spam is bad because users are forced to pay to download content they didnt ask to receive. In many cases users find themselves downloading more spam than legitimate email messages and this dilutes the value of Internet based communication. No-one wants to wade through spam to find the legitimate content.
While ISPs have to bear the bulk of the cost for bandwidth overuse by spammers, this cost is often passed onto the consumer through increased Internet access fees or a degraded service level.
Users themselves are at their wits end, as the process of manually deleting spam is burdensome. Some email clients have special filters which allow for the recognition of spam based on existing messages marked as spam. In addition a number of software companies sell anti-spam software in addition to anti-virus software or content filtering systems.
Spammers generally do not pay much for the sending of spam. They exploit open mail servers to do their task for them. The spammer need only send one email message to an incorrectly configured mail server to reach thousands of email addresses, with the bulk of the transfer being handled by the mis-configured mail server. Recipients in turn need to pay access costs or telephone costs in order to receive content they didnt ask for.
More information can be found here: http://spam.abuse.net/overview/