The government must obtain a valid search warrant before infiltrating your e-mail in a criminal investigation, the Sixth Circuit Court of Appeals has ruled. The appeals court ruled Tuesday on US v. Warshak, noting that e-mail "requires strong protection under the Fourth Amendment," and that law enforcement can't demand for an ISP to give up e-mail with just a court order.

The story behind the case goes back to 2006, when the Feds gained access to e-mail belonging to Steven Warshak, the man behind the "natural male enhancement" product Enzyte. At the time, Warshak had already incurred the wrath of the FTC, which said that there was no evidence that his products worked and found that his company routinely signed up callers for a monthly subscription plan that was difficult to cancel. Soon the FBI and the Postal Inspectors got on Warshak's case for mail and wire fraud as well.

The government was able to gain access to Warshak's e-mail thanks to a court order—a move that requires a significantly lower burden of proof than a full-on warrant. Warshak pushed back on the grounds that the search violated his Fourth Amendment rights. The Sixth Circuit Court of Appeals eventually ruled in Warshak's civil case that his e-mail was indeed Constitutionally protected and that the ability to get the court order without notification was no longer allowed.

Although that previous ruling from the appeals court still stands, the latest decision is related to Warshak's criminal case (he was convicted in 2008 on 93 counts of conspiracy, fraud, and money laundering, and received a 25-year prison sentence). The Sixth Circuit once again agreed that a warrant is necessary before the government can access a citizen's e-mails through an ISP.

"Given the fundamental similarities between e-mail and traditional forms of communication, it would defy common sense to afford e-mails lesser Fourth Amendment protection," wrote the court.

"It follows that e-mail 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," wrote the court. "[T]he ISP is the functional equivalent of a post office or a telephone company. As we have discussed above, 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."

The Electronic Frontier Foundation, which had heavily backed Warshak's position, applauded the latest ruling.

"Today's decision is the only federal appellate decision currently on the books that squarely rules on this critically important privacy issue..." the EFF said in a statement. "We hope that this ruling will spur Congress to update that law as EFF and its partners in the Digital Due Process coalition have urged, so that when the government secretly demands someone's email without probable cause, the email provider can confidently say: 'Come back with a warrant.'"

As for Warshak, the court upheld his criminal conviction but threw out his 25-year sentence, with a remand for resentencing.