It’s often suggested that adding privacy disclaimers to emails is helpful. There is little legal implication to a privacy statement on a regular e-mail. The statement is usually included for professionals with whom a client communication is legally privileged (protected from disclosure in court) – in the case of attorney-client, doctor-patient, etc. When a third party is brought into the conversation, the privilege is destroyed. The disclaimer makes it clear that a transmission to a third party was not intended and the privilege should be maintained. Even at that, it’s not clear that the privilege would be maintained.
Here are some other reasons to have a disclaimer. Consider if any may be important enough to engage company-wide.