A more thorough explanation:

The CAN-SPAM Act of 2003 is a law that regulates commercial email messages. Preemption is a legal concept that means federal law takes precedence over state law. Section 8(b) of the CAN-SPAM Act of 2003 preempts certain state anti-spam laws. This means that some state laws that regulate commercial email messages are not valid if they conflict with the CAN-SPAM Act.

For example, if a state law prohibits the use of certain words in commercial email messages, but the CAN-SPAM Act allows those words, the state law is preempted and cannot be enforced.

However, there are exceptions to preemption. State laws that prohibit fraud or deception in commercial email messages are not preempted. Also, state laws that apply to other types of communication or activity, but also apply to commercial email messages, are not preempted.

For example, if a state law prohibits fraud in all types of communication, including commercial email messages, that law is not preempted by the CAN-SPAM Act.

The issue of CAN-SPAM Act preemption has been addressed by several courts. In one case, a court ruled that a state law was preempted because it penalized non-material errors in commercial email messages. In another case, a court ruled that a university's anti-spam policy was not preempted because it fell under an exception for internet access service providers.