Which email address do notifications use in Teams?

Hi - at the school where I teach we have two forms of email address (for staff)

<staff_name>@<school_name>.school.nz,  and

<staff_name>@apps.<school_name>.school.nz

The first is used to log on to Microsoft applications like Teams and OneNote and the second is for everything Google (sorry!), including Gmail, Classroom etc.

So, when I email notifications working in Teams I expect they will go to the first address.  I'm still working on that from previous post.

However, the students only have a google email address that is active

<student_id>@apps.<school_name>.school.nz

Whilst they have a logon for Microsoft in the form

<student_id>@<school_name>.school.nz

which they use for Teams and OneNote etc, it is not an active email address.  As far as I can tell, the emails to this address simply vanish.

So, how can I get email notifications going to my students in Teams?