What Most Attorneys Now Attach to Email as a Warning:
"NOTICE: This electronic mail message and any attachments may contain attorney-client privileged or otherwise confidential information. Recipients should ensure that proper security measures are taken to maintain any privileged or confidential information. If you are not an intended recipient of this electronic mail message as listed above, please notify The 'Such and Such Law Firm" immediately and delete or destroy the electronic message and all printed copies. The unauthorized disclosure of privileged or otherwise confidential information is strictly prohibited. All recipients are hereby notified that (1) electronic mail is not secure, (2) any electronic mail sent to or received by you may be exposed to multiple computers and/or users in transit, and (3) interception during transit by improper access may occur."
Inadvertent Disclosures by the Attorney or the Client
The above "Notice" is intended to protect from an "inadvertent" disclosure. Each State determines issues of attorney client privilege based on the law of the particular state where the issue is raised. The above warning may or may not protect the privilege in Missouri depending on many factors. As far as can be determined, the Missouri Supreme Court has not ruled on this yet directly. State v. Dandurand, 20 S.W.3d 831 (Mo.banc 2000) discusses inadvertent disclosure in the context of handing over privileged information to an expert for the client and is worth reading. It is my opinion that the "Notice" will not protect you in the event of an interception in light of the very clear warning from the Bar Association. If you really need to send privileged information, the solution is to use a properly secured encryption program. This I believe would, if intercepted (intentionally or unintentionally) and then intentionally "cracked" with some effort with a decryption program would withstand a claim of "no waiver."