Client Not Getting Comment Notification E-mails, but Admin is

I’m working on a blog that has comments required to be approved before showing up. So on the email notifications of new comments, the admin (my co-worker) is receiving the emails. However the post author (the client) is not receiving these same notification emails. They are not in his spam filter, and under user settings, his email address is correct.

Any idea why he wouldn’t receive the notification emails?