Are Your Emails Protected From Warrantless Searches?

An extremely important fight over fundamental privacy rights is heating up as the Department of Justice is pressuring Yahoo to release certain email records under seal. Yahoo, who has been supported in this fight by the Electronic Frontier Foundation and other major corporations such as Google, has so far resisted by claiming the government must first obtain a warrant. The case involves emails from multiple Yahoo user accounts that the government is trying to access. The DOJ is claiming that under the Stored Communications Act once an email has been read it is no longer protected under the law from warrantless searches, and as such, Yahoo should release them.
The Stored Communications Act, 18 U.S.C. Sec. 2703, reads:
A governmental entity may require the disclosure by a provider of electronic communication service of the contents of a wire or electronic communication, that is in electronic storage in an electronic communications system for one hundred and eighty days or less, only pursuant to a warrant issued using the procedures described in the Federal Rules of Criminal Procedure by a court with jurisdiction over the offense under investigation or equivalent State warrant.
The government's argument, which has already been rejected by the 9th Circuit in an earlier case, is that once an email is opened and read, it is no longer in "electronic storage" and thus, not protected by the warrant requirement. The DOJ is in effect saying that your emails are protected under the SCA as long as you never open them or read them. Once the emails are read, the government can force email clients to release them if they are relevant to an investigation.
This case, of course, raises important Fourth Amendment issues as well. After the seminal Fourth Amendment case in 1967,Katz v. US, the government must obtain a warrant to access communications to which the individual has a reasonable expectation of privacy. There are exceptions to this rule as the DOJ will no doubt argue. One exception is that an individual loses that expectation of privacy once the communications are turned over to a third party. It is true that many of our emails are technically turned over to third parties because they are sitting on Yahoo or Google servers. But the same technicality applies to communications over phone lines or by mail, and courts have consistently held these communications to be private. Should the government prevail in this case, it would signal a monumental change in privacy rights for one of our most common forms of communication.
UPDATE: Apparently the DOJ has abruptly halted its pursuit of accessing the Yahoo emails. However, since there was no ruling from the courts the issue remains open for future cases.