A new anti-spam law was passed by the United States and went into effect on January 1, 2004. Under this new law, CAN-SPAM, marketers must remove customers from their lists when requested, they must provide automated opt-out methods as well as complete contact information (address and phone) with alternate means of removal.
CAN-SPAM also bans common spamming practices such as false headers and email harvesting (the use of software that spiders websites to collect email addresses). Subject lines must be truthful and contain a notice that the message is an ad.
CAN-SPAM required truthful email header information (including the from line), accurate subject lines, an opt out tool that works 30 days after mailing, that opt-out requests happen within 10 days, that emails have a physical postal address in all messages, that the messages are labeled as advertisements, and that warnings are displayed for email with sexually oriented material.