Email Notifications on Mailboxes Added Automatically

Hi Everyone 

I have a question im hoping that someone in the community can help me with, I have a client who has multiple mail accounts added to Outlook, my question is as follows: 

There is one mailbox added as my clients own email address and there are others that automatically appear when added to exchange, however

When new mails come in for the main mailbox a banner alert appears perfectly, when other mails are received from other mailboxes that were automatically added through O365 Admin > Exchange, no banners appear

I have tried creating rules for alerts to appear, however only the main mailbox appears as opposed to all multiple accounts seen 

Please could you help suggest anything 🙂