If you use email that is web based (ie "in the cloud") like Gmail or Yahoo!, you may want to know about this.
I recently found out in a magazine article that the antiquated Electronics Communications Privacy Act of 1986 has a provision that makes any email residing on a server over 6 months to be considered abandoned, and is therefor accessible by authorities without a warrant. This covers both personal and corporate email accounts. So, if you or your business uses Google mail for example, any communication over 6 months old is available to law enforcement.
If you live in Kentucky, Michigan, Ohio or Tennessee, then a ruling by the Sixth Circuit of the U.S. Court of Appeals protects you. If you live in the states covered by the other 12 appellate circuits, then this ruling has no effect on you.
I know that unlawful activities documented in email by anyone reading this would never occur, but it never hurts to pass along tidbits when you find them. Happy shredding.