email verification

I have seen a number of posts here with comcast.net email users not receiving verification emails from a variety of senders. The Xfinity official responses keep asking who the sender is and dealing with it like it's a one-off issue. It is not. It is widespread in my experience. I never get them and no, they are not even in my spam folder. Makes me wonder what else I am missing. Is your system blacklisting those? It's a big problem these days since so many sites use verification and if they don't let you choose SMS, you're stuck because comcast.net doesn't send the verification through. 

Please suggest a more comprehensive solution versus looking at individual situations. It happens for most, if not all of these for me.

Thanks.