Sending multiple (thousands/millions) of unsolicited email messages is very cheap. However, the costs for the recipients are considerably greater. These costs can occur at many places along the process of transmitting and delivering email and are closely related to time. Internet Service Providers (ISPs) have an unnecessary load on the processor in their mail servers, reducing performance, slowing access times and displacing normal email. When ISPs are forced to raise rates to cover for an increase in expensive bandwidth, recipients are forced to bear costs that the advertiser has avoided. Many large ISPs have suffered major system outages as the result of massive junk email campaigns.
The methods employed by spammers to avoid being held responsible for their actions are very often fraudulent and tortuous. Numerous court cases are underway between spammers and innocent victims. Many ISPs have set up "filters" to help dispose of unsolicited commercial email. While filters often consume more resources at the ISP, making mail delivery and web surfing slower, they can sometimes help end-users cope a little bit better. Spammers know this, so as they see that mail is being blocked or filtered, the use tricks that help disguise the origin of their messages. One of the most common tricks is to relay their messages off the mail server of an innocent third party. This tactic doubles the damages: both the receiving system, and the innocent relay system are flooded with junk email. And for any mail that gets through, often times the flood of complaints goes back to the innocent site because they were made to look like the origin of the spam. Another common trick that spammers use is to forge the headers of messages, making it appear as though the message originated elsewhere, again providing a convenient target.
A survey in 1999 found that about 17% of typical mail systems allow relaying of mail that is not from or for the system. Such relaying makes it much easier for malicious senders of unsolicited bulk email (UBE) to send their mail without paying any costs. This represents a reduction from 36% a year earlier.
America on Line (AOL) carries in an estimated 30 million email messages each day, about 30% on average was unsolicited commercial email (UCE). The most common UCE appears in the form of: (a) Chain letters; (b) Pyramid schemes (including Multilevel Marketing, or MLM); (c) Other "Get Rich Quick" or "Make Money Fast" (MMF) schemes; (d) Offers of phone sex lines and ads for pornographic web sites; (e) Offers of software for collecting e-mail addresses and sending UCE; (f) Offers of bulk e-mailing services for sending UCE; (g) Stock offerings for unknown start-up corporations; (h) Quack health products and remedies; and (i) Illegally pirated software ("Warez").