Rules of Professional Conduct
Rule 4.4: Respect for Rights of Third Persons
(a) In representing a client, a lawyer shall not use means that have no substantial purpose other than to embarrass, delay, or burden a third person, or knowingly use methods of obtaining evidence that violate the legal rights of such a person.
(b) A lawyer who receives a writing relating to the representation of a client and knows, before examining the writing, that it has been inadvertently sent, shall not examine the writing, but shall notify the sending party and abide by the instructions of the sending party regarding the return or destruction of the writing.
 Responsibility to a client requires a lawyer to subordinate the interests of others to those of the client, but that responsibility does not imply that a lawyer may disregard the rights of third persons. It is impractical to catalogue all such rights, but they include legal restrictions on methods of obtaining evidence from third persons and unwarranted intrusions into privileged relationships, such as the client-lawyer relationship.
 Paragraph (b) addresses the obligations of a lawyer who receives writings containing client secrets or confidences in material delivered by an adversary lawyer and who knows that the sending lawyer inadvertently included these writings. As the D.C. Legal Ethics Committee noted in Opinion 256, this problem is “an unfortunate (but not uncommon) consequence of an increasingly electronic world, as when a facsimile or electronic mail transmission is mistakenly made to an unintended recipient.” Consistent with Opinion 256, paragraph (b) requires the receiving lawyer to comply with the sending party’s instruction about disposition of the writing in this circumstances, and also prohibits the receiving lawyer from reading or using the material. ABA Model Rule 4.4 requires the receiving lawyer only to notify the sender in order to permit the sender to take protective measures, but Paragraph (b) of the D.C. Rule 4.4 requires the receiving lawyer to do more.
 On the other hand, where writings containing client secrets or confidences are inadvertently delivered to an adversary lawyer, and the receiving lawyer in good faith reviews the materials before the lawyer knows that they were inadvertently sent, the receiving lawyer commits no ethical violation by retaining and using those materials. See D.C. Legal Ethics Committee Opinion 256. Whether the privileged status of a writing has been waived is a matter of law beyond the scope of these Rules. Similarly, this rule does not address the legal duties of a lawyer who receives a writing that the lawyer knows or reasonably should know may have been wrongfully obtained by the sending person. See D.C. Bar Legal Ethics Committee Opinion 318.