What happened in the case was that the government forced an ISP to reveal 27,000 emails without securing a warrant or giving notice to the customer, Steven Warshak. The Sixth Circuit Court held that the seizure violated Warshak’s Fourth Amendment rights because they were allowed to so because of the Stored Communications Act. Ironically, that act was meant to prohibit ISPs and other electronic communication providers from sharing mail or messages without their senders or receivers’ permission.
To quote from the Court’s decision:
Given the fundamental similarities between email and traditional forms of communication [like postal mail and telephone calls], it would defy common sense to afford emails lesser Fourth Amendment protection … It follows that email requires strong protection under the Fourth Amendment; otherwise the Fourth Amendment would prove an ineffective guardian of private communication, an essential purpose it has long been recognized to serve.
“The police may not storm the post office and intercept a letter, and they are likewise forbidden from using the phone system to make a clandestine recording of a telephone call — unless they get a warrant, that is. … It only stands to reason that, if government agents compel an ISP to surrender the contents of a subscriber’s emails, those agents have thereby conducted a Fourth Amendment search, which necessitates compliance with the warrant requirement.