"It shows resourcefulness, too, because the candidate often has to hunt down an email address the interviewer never gave them."

So basically the author expects the candidate to send a thank you email even though she didn't exchange her email address. Well, I think such email is natural when you make a personal contact with the interviewer, but in this scenario(when you receive emails from noreply@bigcorporate.com) it feels unnecessary and intrusive to me.