s2Member Thank you login email not making it to inbox

Hi, I have my wordpress account set up with s2Member pro. I am using Clickbank as a payment processor. It is all integrated correctly. But I noticed when I do multiple test purchases although the Clickbank receipt always arrives in the email inbox, the “Thank” you email from s2Member only arrives sporadically…for example if I do 10 test purchases on 10 different products the s2member email only arrives maybe 3 out of 10 times. This could be an issue with real customers who never receive the s2Member Thank You login email. They can click on the “Access Digital Product” once in the Clickbank receipt to either access the s2member restricted protected page, or click on it to register a username and password to access a s2member protected Levels page. After that the button in the Clickbank is obsolete. They need the Thank you email from s2member to get the tinyurl link for the protected page they purchased access to. Otherwise they will have to save/bookmark/favorite the original link or copy it and most won’t do that even if instructed. Same with writing their username and password. So the point is I contacted both Clickbank about their ipn, and my web server host, and both said to contact s2member support. I have not heard from support about this issues via email so I signed up here. Any help would be great. I have tested both Clickbank ipn 2.1 and 6.0, same issue in s2Member…but not sure if it is a s2Member issue. Just asking.