A more thorough explanation:

Gordon v. Virtumundo is a legal case that dealt with spam emails and the laws surrounding them. The plaintiff, James S. Gordon, Jr., sued Virtumundo, Inc. and Adknowledge, Inc. for sending him spam emails. He argued that their spamming activity violated the CAN-SPAM Act of 2003, Washington's Commercial Electronic Mail Act (CEMA), Washington's Consumer Protection Act, and Washington's "Prize Statute".

The Ninth Circuit held that Gordon lacked standing to bring claims under the CAN-SPAM Act because he was not an "internet access service provider" and he was not "adversely affected" by violations of the CAN-SPAM Act. The court noted that the purpose of the CAN-SPAM Act was not to completely eliminate spam, but to target "deceptive and predatory" commercial email practices. Congress conferred standing to bring CAN-SPAM lawsuits on a "narrow group of possible plaintiffs" who are "well-equipped to efficiently and effectively pursue legal actions against persons engaged in unlawful practices and enforce federal law for the benefit of all consumers." The court also held that Gordon's claims under Washington's CEMA were preempted by the CAN-SPAM Act because they did not fit within the CAN-SPAM Act's limited exception to preemption.

If a person receives spam emails, they cannot sue the sender under the CAN-SPAM Act unless they are an "internet access service provider" and are "adversely affected" by the spam. This means that the person must have a technical or hardware component that is affected by the spam, and the harm must exceed "the ordinary inconveniences experienced by consumers and end users."

The court held that Gordon's CEMA claims were preempted by the CAN-SPAM Act because they did not fit within the CAN-SPAM Act's limited exception to preemption. Congress intended the CAN-SPAM Act to broadly preempt state regulation of commercial email, and intended to allow only a narrow exception for state laws targeting fraud or deception in commercial email communications. Interpreted in light of these CAN-SPAM Act preemption principles, CEMA claims relating to "header" information (e.g. domain names) must be substantiated with evidence of actual fraud or deception, analogous to what would be required in a traditional tort case.

If a person wants to sue a sender of spam emails under CEMA, they must provide evidence of actual fraud or deception in the email header information. If the header information is incomplete or difficult to identify with a particular sender, the claims will not survive preemption analysis.