When a lawyer (the “sending lawyer”) copies the lawyer’s client on an electronic communication to counsel representing another person in the matter (the “receiving counsel”), the sending lawyer creates a group communication. This group communication raises questions under Rule 4.2’s “no contact” rule because of the possibility that the receiving counsel will Reply-to-All, which of course will be delivered to the sending lawyer’s client.
Unsurprisingly, the ABA Standing Committee opines that the sending lawyer impliedly consents to receiving counsel’s Reply-to-All response that includes the sending lawyer’s client.
The Formal Opinion does, at the same time, include a few caveats: First, an express written or oral remark informing receiving counsel that the sending lawyer does not consent to a Reply-to-All communication would override the presumption of implied consent. Second, the presumption applies only to emails or similar group electronic communications, such as text messaging, which the lawyer initiates; it does not apply to other forms of communication, such as a traditional letter printed on paper and mailed. Finally, although the act of Replying-to-All is generally permitted under Rule 4.2, other Rules restrict the content of that reply. (see, e.g., Rule 4.4(a) (generally prohibiting unwarranted intrusions into privileged relationships, including the attorney-client relationship); Rule 4.4(b) cmt.  (“If a lawyer knows or reasonably should know that an email was sent inadvertently, then this Rule requires the lawyer to promptly notify the sender in order to permit that person to take protective measures”); Rule 8.4(c) (prohibiting counsel from making misrepresentations).
ABA Formal Opinion No.503 (Nov. 2, 2022).