Students cannot receive email notifications

I have already verified that all students have their Google Classroom settings set to "allow email notifications" and every possible option is turned on. They have turned it off, logged out, logged back in, turned it on, logged out, logged back in, cleared their Chrome cache (we always use Chrome as the browser), there is nothing in their Spam folder, nothing changes.

I'm a teacher, but also the main admin for our small school's G Suite - I know just enough to be dangerous!

We have a handful of organizational groups all under one domain.  Students is one of those organizational groups and we have restricted delivery to that group (settings found in the apps>Google Workspace>Settings for Gmail>Compliance).

Since we do not want students receiving email from outside our domain, we restrict delivery from only three sources:

1. The domain our school uses
2. The google bounce message (email: mailer-daemon@googlemail.com)
3. I recently added the domain classroom.google.com.  

I added the last domain because that is the Google Classroom domain from where I receive my notifications that students have turned in work, commented, etc. I saw in another help thread that someone added this domain and was able to reestablish notifications for their students.  It has been over 24 hours since I added #3 above and nothing has changed for my students, they still are receiving no notifications.

Can anyone help out?

Thanks,

David