Log into your Office 365 account via a web browser, go to the nine dots in the top left of the screen and select “Outlook”.
From Outlook, go to your name in the top right of the screen and click “Open another mailbox”.
Type the name of your inbox into the box that appears and click open.
This will open the mailbox in a new tab and you should be able to see every email sent to this mailbox, rather than the normal 12 months in Outlook.