First class domestic mail may be opened, and the contents inspected, only (1) with the authorization of the addressee, (2) pursuant to a valid search warrant authorized by law, or (3) by an officer or employee of the Postal Service for the sole purpose of determining an address at which the mail can be delivered.134
A different federal statute applies to mail originating outside the United States. Under this statute a customs officer or other person authorized to board or search vessels may "search any . . . envelope, wherever found, in which he may have a reasonable cause to suspect there is merchandise which was imported contrary to law . . . ."135
The Postal Service regulates permissible use of the "mail cover," an investigative procedure whereby government officials record information appearing on the exterior of first class mail, and information regarding both the exterior and contents of lower classes of mail. Under Postal Service regulations, the government may use mail covers only to protect national security; locate a fugitive; obtain evidence of commission or attempted commission of a crime; obtain evidence of a violation or attempted violation of a postal statute; or assist in the identification of property, proceeds or assets forfeitable under law.136 Furthermore, law enforcement agencies must submit mailcover requests to the Post Office in writing, setting forth reasonable grounds to believe the mail cover is necessary for one of the enumerated purposes.137
134. 39 U.S.C. § 3623(d) (1994).
135. 19 U.S.C. § 482 (1994).
136. 39 C.F.R. § 233.3 (1994).
137. There are limited exceptions to this requirement, such as for situations involving recovery of stolen mail, dealing with damaged mail, or involving an immediate threat to persons or property. See 39 C.F.R. § 233.3(f).