The problem is that most mobile networks use CGNAT, this means that the 'real' public IP is shared between many users. It only takes one bad player and the shared IP gets a poor reputation.
I used to go to Portugal in the winter for a few weeks and many of the rentals used mobile broadband. I would often hit the problem of not being able to send for a day or two. Latterly the villa we rented changed to a cable connection and the problem no longer existed.
The SMTP protocol does return an error code which identifies the cause, however most email clients don't expose it, rather they just return an error of 'failed to send' often with a username/password reason
Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.
