When it comes to telephone calls, government investigators can usually get access only with a search warrant issued by a court.

Email, however, is a different story. Under the 1986 Electronic Communications Privacy Act, a search warrant based on probable cause is required to gain access to email messages stored for 180 days or less on the servers of an Internet service provider, such as Google or Yahoo. Older messages, however, can be demanded with a subpoena.

...