The United States Supreme Court rejected the control group test in Upjohn v. United States, 449 U.S. 383 (1981). Most courts now apply the Supreme Court's reasoning in that case to corporate privilege claims, including those involving former employees.
The lawyer-client privilege protects your communications even after the attorney-client relationship ends. Even if you fire your attorney or they terminate the relationship for not paying their fees, they still cannot reveal anything you told them in confidence.
A waiver can occur from a variety of conduct that fails to maintain the confidentiality of the communication. Either voluntary or inadvertent disclosure to outside or non-covered recipients, professional advisors outside the privilege, and experts and consultants, can result in waiver as a matter of law.
The protections of the attorney-client privilege survive indefinitely. This means that the protections remain in place even when the attorney-client relationship ends, no matter if the relationship ends due to voluntary termination or due to the death of one of the parties.
Imminent death or harm. Your attorney can't be held to attorney-client privilege if they believe that keeping your confidence would result in death or significant physical harm to someone.
Crime or Fraud Exception. If a client seeks advice from an attorney to assist with the furtherance of a crime or fraud or the post-commission concealment of the crime or fraud, then the communication is not privileged.
It is a common practice for outside litigation counsel to represent current, and even former, employees of corporate clients during depositions. This practice, however, is governed by ethical rules (and opinions and case law) that must be considered in advance.
There are two major exceptions to the lawyer-client privilege under the California Evidence Code, as discussed below. 2.1. Crime or fraud. 2.2. Preventing death or substantial physical harm.
The privilege extends only to communications that the client intends to be confidential. Communications made in non-private settings, or in the presence of third persons unnecessary to accomplish the purpose for which the attorney was consulted, are not confidential and therefore are not protected by the privilege.
To be safe put "Attorney-Client Communication", "Privileged and Confidential" or "Attorney Work Product" in the subject of the e-mail, or on privileged documents.