The 6th U.S. Circuit Court of Appeals found that e-mail users have a reasonable expectation that their stored e-mail will be as private as a telephone call.
http://informationweek.com/news/showArticle.jhtml?articleID=199905509
http://www.ca6.uscourts.gov/opinions.pdf/07a0225p-06.pdf (decision)
us: No E-mail Searches Without Warrants, Federal Judge Says
The 6th U.S. Circuit Court of Appeals found that e-mail users have a reasonable expectation that their stored e-mail will be as private as a telephone call.