Jack Shafer fisks an email disclaimer. It’s not really a fair fight.
I see his point – disclaimers on email messages are hardly ironclad legal protection – but any careful lawyer will tell you that you’re better off trying. In some contexts, such as protection of the attorney-client privilege, courts will look at what steps you took to keep things confidential – and having a disclaimer, while hardly determinative, can’t hurt. Granted, it’s hard to argue that something a computer stamps on every outgoing message is an indicia of the privileged nature of the contents, but it’s at least a sign that you are notifying an inadvertent recipient that this could be sensitive stuff they should give back.