From Dissenter.com: The American Civil Liberties Union (ACLU) has received documents in response to a Freedom of Information Act (FOIA) request that provide details on FBI and Justice Department policies, which appear to suggest the federal authorities can read emails without obtaining a warrant.
The FBI provided a copy of a 2012 Domestic Investigations and Operations Guide (DIOG) that had not been made public. It contained nothing about the Fourth Amendment requiring a warrant for all emails.