According to the Federal Trade Commission, the CAN-SPAM Act is a law by the US government, which sets the rules for commercial emails, establishes requirements for commercial messages, gives recipients the right to stop you from emailing them, and spells out tough penalties for violations. The CAN-SPAM Act is defined as Controlling the Assault of Non-Solicited Pornography and Marketing Act.
Each separate email you send which does not follow this law may subject you to a penalty up to $42.53.
Details in your commercial messages should be clear and truthful: subject line, email addresses, and domain name, and "To" and "From".
Emails that are sent for advertising purposes must be clear and indicated as an ad.
Messages containing sexual content must contain “SEXUALLY-EXPLICIT” warnings at the beginning of the email subject line. Also, the information needs to be viewable only upon opening the message.
Emails must contain a valid, registered postal address every time.
Under the legislation, subscribers have the right to opt-out from your email list at any time, so the opt-out opportunity has to be presented in every email.
Here is an example of CAN-SPAM compliant email;
Here is an example of CAN-SPAM non-compliant email;