Yahoo and federal prosecutors in Colorado are embroiled in a privacy battle that's testing whether the Constitution's warrant requirements apply to Americans' e-mail.

The legal dust-up, unsealed late Tuesday, concerns a 1986 law that already allows the government to obtain a suspect's e-mail from an ISP or webmail provider without a probable-cause warrant, once it's been stored for 180 days or more. The government now contends it can get e-mail under 180-days old if that e-mail has been read by the owner, and the Constitution's Fourth Amendment protections don't apply.

Yahoo is challenging the government's position and defying a court order to turn over some customer e-mail to the feds. Google, the Electronic Frontier Foundation, the Center for Democracy & Technology and other groups late Tuesday told the federal judge presiding over the case that accessing e-mail under 180 days old requires a valid warrant under the Fourth Amendment, regardless of whether it has been read.

"The government says the Fourth Amendment does not protect these e-mails," Kevin Bankston, an EFF lawyer, said in a telephone interview Wednesday. "What we're talking about is archives of our personal correspondence that they would need a warrant to get from your computer but not from the server."

If the courts adopt the government's position, the vast majority of Americans' e-mail would be accessible to the government without probable cause, whenever law enforcement believes the messages would be relevant to a criminal investigation, even if the e-mail's owner is not suspected of wrongdoing.

The legal jockeying began Dec. 3, when a Colorado magistrate ordered Yahoo to hand over to authorities e-mail communications under six months old "received by the specified accounts that the owner or user of the account has already accessed, viewed, or downloaded."

Yahoo refused, claiming the Stored Communications Act requires the government to show probable cause to obtain that e-mail. The government asserted a lesser, warrantless standard that the "communications sought are relevant and material to an ongoing criminal investigation."

The difference between those standards is the subject of fierce debate in the legal community.

But all sides agree that obtaining unopened e-mail less than 180 days old requires the authorities to make a probable-cause showing to a judge, and that after 180 days stored e-mail – read or unread – can be accessed without such a warrant.

The 1986 Stored Communications Act was enacted at a time when e-mail generally wasn't stored on servers at all, but instead passed through them briefly on their way to the recipient's inbox. In today's reality, e-mail can, and is, being stored on servers forever. A consortium of businesses, including Google and Microsoft, recentlyasked Congress to update the law and require probable cause to obtain any e-mail.

But the government's position in the Colorado case pushes the outdated law even further. Prosecutors are arguing that opened e-mail less than 180 days old is no longer in "electronic storage" as defined by the law – which allows the feds to obtain it with the lower standard.

The 1986 law defines electronic storage as "(A) any temporary, intermediate storage of a wire or electronic communication incidental to the electronic transmission thereof; and (B) any storage of such communication by an electronic communication service for purposes of backup protection of such communication."

The government, in urging the Colorado court to compel Yahoo to comply, wrote in in a brief unsealed Tuesday that "[s]torage of previously opened e-mail (.pdf) does not fall within the subsection (A) of this definition because its storage is no longer temporary, intermediate, or incident to transmission. It does not fall within the subsection (B) of this definition because that subsection includes only copies of electronic communications stored by a service provider for its backup protection."

In response, Yahoo said in a Tuesday unsealed court filing that the distinction is immaterial, "misguided" (.pdf) and settled in a recent civil case.

The EFF, Google and CDT asserted in its filing that all e-mail – regardless of its age or whether it was opened – should be subject to a probable-cause warrant. "The Fourth Amendment protects stored e-mails (.pdf) just as it does conversational privacy and private papers."

The nature of the criminal case is under seal. The only available public record of the case concerns the constitutional issues surrounding the Stored Communications Act. All three of those filings are linked above.

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