I am the primary host in communication with guests, but my co-host used to get all the same emails I do. He no longer gets any of them. I haven't changed any settings. What might be the problem?
Ask your co-host to go to "account" and then "notifications" and make sure that the boxes that they want are checked. This is where they would nominate to receive emails or sms messages. Maybe they could try to untick the boxes and save and then retick and save and see if that helps.