In the U.S., there are some laws that protect the privacy of email.

The first is the Wiretap Act, codified under 18 U.S.C. 2510 et al.. The definitive case is U.S. v. Councilman 418 F.3d 67 (Fed. 1st Cir. 2005). See also the amicus brief in the Councilman case filed by Senator Patrick Leahy, one of the authors of the Electronic Communications Privacy Act, which amended the Wiretap Act to protect electronic communications like email. The Electronic Privacy Information Center (www.epic.org) has more information on the Councilman case, and includes all the briefs and Court decisions.

The second is the Electronic Communications Privacy Act, codified under 18 U.S.C. 2701 et al.

The third is the Sheman Anti Trust Act. A helpful case is Exactis v. Mail Abuse Prevention System, frequently referred to as Exactis v. MAPS. The case is interesting for the TRO that was granted to Exactis. See the MAPS story. Exactis asserted a per se violation of section 1 of the Sherman Action (15 U.S.C 1)

http://www.usdoj.gov/atr/foia/divisionmanual/two.htm