Nearly every case focusing on inadvertently disclosed privileged communications (during document productions or at other times) focuses on the privilege waiver implications. However, the stakes can be much higher.
McDermott Will & Emery LLP v. Superior Court, 217 Cal. Rptr. 3d 47 (Cal. Ct. App. 2017), one member of a feuding family accidentally emailed a privileged communication to the other side of the family. That document eventually fell into the hands of Gibson Dunn, which represented the other side's ally. The trial court concluded that the accidental email disclosure did not waive the privilege – and then disqualified Gibson Dunn for having read and relied on the inadvertently disclosed document. The appellate court agreed.
Unless there is a need for speed, lawyers receiving an adversary's obviously privileged communications (during document productions or at other times) normally would be wise to wait until a court deals with the privilege waiver issue before reading or relying on them.