A more thorough explanation:

The CAN-SPAM Act is a law passed by Congress in 2003 to regulate spam email. The law sets a national standard for the regulation of spam email and prohibits the inclusion of deceptive or misleading information and subject headings. It also requires identifying information such as a return address in email messages and prohibits sending emails to a recipient after an explicit response that the recipient does not want to continue receiving messages (i.e. an "opt-out").

The Act also "preempts" (supersedes) state laws that regulate the sending of commercial email. However, state laws prohibiting fraud or deception in the content of email or email attachments won't be preempted. Principles of federalism applied to the interpretation of this section of the Act will also protect some state laws from being preempted. The question as to what specific state laws are preempted, and to what extent they are preempted, is one that will ultimately be worked out in the courts.

• Sending an email with a misleading subject line, such as "You've won a prize!" when the recipient has not actually won anything, would be a violation of the CAN-SPAM Act.
• Not including a return address in an email message would also be a violation of the Act.
• If a recipient explicitly requests to stop receiving emails from a sender, the sender must honor that request and stop sending emails to that recipient.

These examples illustrate how the CAN-SPAM Act regulates the content and sending of commercial emails to protect consumers from deceptive or unwanted messages.