Not receiving email from two specific addresses (maybe more???)

I am not receiving emails from a sender at the following two domains:

 @firsttechfed.com

 @crutchfield.com

In both cases, the sender eventually sent the same email to both my comcast.net and gmail.com addresses. In both cases, I only received the email through the gmail.com domain. These emails sent to my comcast.net address do not bounce, and are not delivered to my Inbox or Spam folder.

 

What is the cause? Can this be corrected? And, just as important, what other emails may I be missing? How would I know???