Spam is in several ways not harmless. The least it does is taking away bandwidth from the internet users. By 2004 over 30% of all internet traffic is consumed up by spam.
Also consider that each e-mail cost in average the equivalent energy of 50 grams of coal, a lot of energy is wasted here. (quote from anonymous source) In this light it is un-understandable that there is done almost nothing against it.
And it gets worse and worse. Polluting one's mailbox and sometimes snow under messages you do want to receive. In volume spam can take up from 1 or 5 messages a day to almost 99% of you mail box. That of course is depending on how visible you are on the internet.
The original purpose of spam is selling or promoting an article. In the past several years Viagra, penis enlargers, libido enhancers, are the most popular items. Another list can be made of mortgage offerings, lending, offers to alleviate your loans or credit card burden. And lately spam offers nothing in particular but to visit some specific site mostly with content as the above.
It gets harder and harder to recognize spam because most messages appear to be quite normal with ordinary sender names and subjects. Even spam filters think the mail with a nonsensical (re: idiotic) contents are regular e-mail. But installing spam filters forces you to choose between speed over convenience. The tighter your screening is the more risk you have to filter out legitimate mail or slow down your email processing. The latter is the case with virus filtering. How most filters work can be abundantly found on the Internet.
How Spammers work
Many spammers can buy a database from companies with millions of valid email addresses and use them to advertise. These email addressees are composed of addresses used on newsgroups and chat rooms. Many companies have special software that can extract these addresses and put them into a database to sell. Many companies also search the web, looking for web addresses with the symbol @ at the end. From these, they can find valid email addresses. Many of these types of companies work outside countries with legislation against spamming in order to avoid lawsuits. According to Marshall Brain quoting "Detroit Free Press: Spam king lives large off others' e-mail troubles".
Typical spamming company often works like this:
The computers in Ralsky's basement control 190 e-mail servers -- 110 located in Southfield, 50 in Dallas and 30 more in Canada, China, Russia and India. Each computer, he said, is capable of sending out 650,000 messages every hour -- more than a billion a day -- routed through overseas Internet companies Ralsky said are eager to sell him bandwidth.
Many spammers can make up to $700 per hour by simply using lists of email addresses and applying them to their advertisement. As spam celebrates it's 25th year of operation, we must remember that spam takes up about 40% of all email messages sent on the web. How can we prevent this even further?