May sound silly, but make sure you didn't misspell Yip's email address. Common mistake that has happened to all of us at some point.
If your emails did not bounce, it might be a spam filter problem. Most email providers have spam filters that filter emails based on the domain name. If your domain is anything fancier than yahoo, gmail, hotmail, etc., it is possible that his filter thinks your emails are junk and never make it to his inbox.
If your emails did not bounce, it might be a spam filter problem. Most email providers have spam filters that filter emails based on the domain name. If your domain is anything fancier than yahoo, gmail, hotmail, etc., it is possible that his filter thinks your emails are junk and never make it to his inbox.