In the absence of detained regulations or case law, standards for what is clear and conspicuous can change over time. Since Congress passed the U-CAN-SPAM Act, your customers have had 18 years to learn how things work. If they're plagued by spam that gets through filters, they've learned how to unsubscribe from its sources. In 2003, I would have agreed with Randy. Today...I'm not so sure.
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...gone fishing.