Under current law, via EPIC:

Here's a 2009 Government chart showing the different requirements.

There is a growing consensus that greater protections are needed.

The Electronic Communications Privacy Act (ECPA), which has not had an update since it passed in 1986, specifies that government officials do not need a warrant to access stored email that is over 180 days old. The Department of Justice has also historically argued ECPA grants law enforcement the authority to access opened email without a warrant.

When ECPA was passed in 1986, email storage was much more expensive than it is today. The few people who actually used email would download important messages to their hard drives. Emails that were stored online for more than 180 days were considered abandoned, and therefore did not receive warrant protection. In 2013, users have access to free, nearly unlimited online email storage, rendering the 180-day provision woefully unsuited to the times.

The ECPA has three parts:

• the Wiretap Act, 18 U.S.C. S. 2510 et seq.,
• the Pen Register and Trap and Trace Devices Act 18 U.S.C. S. 3121, et seq., and
• the Stored Communications Act ("SCA"), 18 U.S.C. S. 2701 et seq.
  

The Stored Communications Act (“SCA”) addresses the ability of governmental entities to compel service providers, such as Twitter and Facebook, to produce content (e.g., posts and tweets) and noncontent customer records (e.g., name and address).

§ 2703 states the procedure federal and state law enforcement officers must follow to compel disclosure of stored communications from network service providers.

The Leahy bill would repeal sections (a)(b) and © of 2703 and eliminate the 180 day rule.

Section 5 of Leahy's bill provides:

Nothing in this Act or an amendment made by this Act shall be construed to apply the warrant requirement for contents of a wire or electronic communication authorized under this Act or an amendment made by this Act to any other section of title 18, United States Code (including chapter 119 of such title (commonly known as the 18 ‘‘Wiretap Act’’)), the Foreign Intelligence Surveillance Act 19 of 1978 (50 U.S.C. 1801 et seq.), or any other provision 20 of Federal law.

More news articles on the bill here and here.

The bill now moves to the full Senate.