Email not received

Email not received

Dear Zoho Team,

I'm having a strange issue where one specific kind of email is not showing up in my inbox or SPAM. All other emails are being delivered fine. These are "test" emails sent from an online course company called Teachable. I have trouble-shooted with their IT team and they claim that the emails are appearing as "sent" on their end. They said " I do see that your emails are successfully being delivered. Here's an image of the mail log for context:"
and provided the following two images to verify this: 

https://teachable.zendesk.com/attachments/token/b8XhgH2Mgc7zYU1zsPI83VMuJ/?name=Image+2017-09-17+at+10.22.24+AM.png
https://teachable.zendesk.com/attachments/token/08RadHLQihMObfbqhbf4FCfwl/?name=Image+2017-09-17+at+10.25.00+AM.png

I used to receive these emails correctly with no problem, but at a certain point they stopped being delivered / appearing in my inbox. I am at a loss of what to do or how to trouble shoot. Can you please advise??

Many thanks,
Oren J. Sofer