The CAN-SPAM Act is a U.S. law that sets the rules for commercial email, establishes requirements for commercial messages, and gives recipients the right to have you stop emailing them. It's crucial because violating the CAN-SPAM Act can result in significant penalties. Compliance involves ensuring that your emails do not contain misleading header information or deceptive subject lines, and that you include a valid physical postal address and a clear opt-out mechanism.