With our without the backing of the Fourth Amendment, we don't recommend incriminating yourselves via email, but for what it's worth, the Sixth Circuit Court of Appeals did rule that Uncle Sam needs a search warrant before he goes snooping in your inbox, the Electronic Frontier Foundation reports . Here's what the Court had to say:
"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.... [T]he 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...."
The EFF called the ruling a landmark decision, noting that it's the "only federal appellate decision currently on the books that squarely rules on this critically important privacy issue."