CAN-SPAM Act Basics
"The CAN-SPAM Act of 2003 (Controlling the Assault of Non-Solicited Pornography and Marketing Act) establishes requirements for those who send commercial email, spells out penalties for spammers and companies whose products are advertised in spam if they violate the law, and gives consumers the right to ask emailers to stop spamming them.
The law, which became effective January 1, 2004, covers email whose primary purpose is advertising or promoting a commercial product or service, including content on a Web site. A 'transactional or relationship message' - email that facilitates an agreed-upon transaction or updates a customer in an existing business relationship - may not contain false or misleading routing information, but otherwise is exempt from most provisions of the CAN-SPAM Act.
The Federal Trade Commission (FTC), the nation's consumer protection agency, is authorized to enforce the CAN-SPAM Act. CAN-SPAM also gives the Department of Justice (DOJ) the authority to enforce its criminal sanctions. Other federal and state agencies can enforce the law against organizations under their jurisdiction, and companies that provide Internet access may sue violators, as well."
Read more in this CAN-SPAM Act summary from the FTC.