Everything gets tested at the extremes, but for the most part, email disclaimers are there as minor CYA measures for the sender of the email. Lawyers use them all the time, for instance, so that nobody misinterprets their daily chatter or off-the-cuff advice as constituting an official attorney-client relationship with the recipient.

Obviously you can't hide behind an email disclaimer to C your A if your A is blatantly violating the letter or spirit of the disclaimer.