From FourthAmendment.com, an excerpt from the opinion in Commonwealth v. Delgado-Rivera, 2021 Mass. LEXIS 341 (June 1, 2021):
The record here, and the relinquishment of control it represents, is important because “the Fourth Amendment does not protect items that a defendant ‘knowingly exposes to the public.’” Dunning, 312 F.3d at 531, citing United States v. Miller, 425 U.S. 435, 442, 96 S. Ct. 1619, 48 L. Ed. 2d 71 (1976). The judge sought to distinguish between communications that have been shared with a particular individual, such as the intended recipient, and communications that are released “more generally … [in a way] in which [they] can be discovered by members of the public or police or anyone else.” This distinction is not persuasive. “It is well settled that when an individual reveals private information to another, [the individual] assumes the risk that his [or her] confidant will reveal that information,” frustrating the sender’s original expectation of privacy and, in effect, making this once-private information subject to disclosure without a violation of the sender’s constitutional rights. United States v. Jacobsen, 466 U.S. 109, 117, 104 S. Ct. 1652, 80 L. Ed. 2d 85 (1984). In the circumstances here, Delgado-Rivera assumed the risk that the communications he shared with Garcia-Castaneda might be made accessible to others, including law enforcement, through Garcia-Castaneda and his devices. See Alinovi v. Worcester Sch. Comm., 777 F.2d 776, 784 (1st Cir. 1985), cert. denied, 479 U.S. 816, 107 S. Ct. 72, 93 L. Ed. 2d 29 (1986).
Read more about the opinion and its rationale on FourthAmendment.com