It can't provide confidence that the message comes from the right/real person, because even without any breach of secrets (which happen even to competent people/organizations) all that gives you is confidence that the message comes from someone authorized by that right/real person. It could be another person, or it could be data generated by an automated system to which they gave the credentials for whatever reason - historically rich people used personal secretaries for writing all kinds of responses including personal ones ("I'm so grateful for your invitation to visit, let's ..." didn't necessarily mean that the actual person even read your invitation), and if an "artificial secretary" becomes good enough, people will use it in future.