UNITED STATES V. MOHAMUD 45 ii. Mohamud’s Privacy Interest The parties agree that Mohamud had some expectation of privacy in his electronic communications, but disagree as to the strength of his interest. The government argues that U.S. persons have a limited expectation of privacy when communicating electronically with non-U.S. persons located outside the United States because of the Fourth Amendment’s “third-party” doctrine—that a person’s privacy interest is diminished where he or she reveals information to a third party, even in confidence. Mohamud contends that the voluntary disclosure of information to third parties does not reduce the expectation of privacy. The district court determined that under the third-party doctrine, Mohamud had a reduced expectation of privacy in his communications to third parties. We agree. With respect to a U.S. person’s privacy interest, we treat emails as letters. See, e.g., [Redacted], 2011 WL 10945618, at *26 (FISA Ct. Oct. 3, 2011) (“Whether they are transmitted by letter, telephone or e-mail, a person’s private communications are akin to personal papers.”); United States v. Warshak, 631 F.3d 266, 285–86 (6th Cir. 2010) (“Given the fundamental similarities between email and traditional forms of communication, it would defy common sense to afford emails lesser Fourth Amendment protection.”). Accordingly, until electronic communications reach the recipient, they retain the same level of privacy interest as if they were still in the home. See, e.g., United States v. Van Leeuwen, 397 U.S. 249, 251 (1970). But as with letters, “[a] person’s reasonable expectation of privacy may be diminished in ‘transmissions over the Internet or e-mail that have already arrived at the recipient.’”