As a new President faces a whole host of civil liberties issues upon taking office, one that looms large is communications privacy. Still unresolved from the previous administration are the legality of President Bush's so-called Terrorist Surveillance Program and the constitutionality of the Foreign Intelligence Surveillance Act. Embedded in those important questions is a question about the sanctity of the nation's oldest and most venerable means of long-distance communications, the mail. That question is whether the government may open first-class mail without a warrant and, if so, under what circumstances. In this short article, I analyze the regulatory, statutory, and constitutional issues related to that question. I conclude that the statutory prohibition on mail opening only applies to mail matter that falls into the category of "letter" - which, roughly speaking, is defined as a "message" or "communication" or "correspondence." The prohibition on mail opening does not apply to mail matter other than "correspondence," such as bombs, anthrax or any ordinary good. The statute bars the opening of letters without a warrant, subject only to one relevant exception: the "physical searches" provisions in the Foreign Intelligence Surveillance Act ("FISA"). The government may not open letters without either a warrant or following the procedures set forth in FISA. There is no "exigent circumstances" exception for letters, though the government may temporarily detain a letter for the purpose of obtaining a warrant. On the other hand, the government may open other mail matter without a warrant subject only to the strictures of the Fourth Amendment. The Fourth Amendment does contain an "exigent circumstances" exception to the ordinary rule that a warrant is required. Thus, scenarios that might involve hazardous materials such as anthrax or a ticking time bomb would in many circumstances fall into this exception.