It does seem like a footer along the lines of

This message is not intended as legal advice. I am not your lawyer.

added to emails from lawyers or other law firm employees casually discussing legal issues could prevent the accidental creation of an attorney/client relationship. Something similar might help prevent liability for medical professionals trying to be helpful.

Of course, the vast majority of these are pointless and annoying. It's not usually possible to impose any legal obligations on someone simply by sending them an email.