There are a couple of ways that you can access a shared mailbox after logging in Office 365 Outlook Web Access (https://outlook.com/owa/derby.ac.uk)
Please ensure you go into the 'Mail' app before following these instructions.
To Open the Mailbox in a new Window
1. Click the 'person' icon in the top right,
2. Select Open another mailbox.
3. Enter the full name of the mailbox (including the '@derby.ac.uk' suffix) in the text box.
4. Click Open
To Add the mailbox to your folder list in the same Window
When you are signed in to the Office 365 Outlook WebAccess, in the folder menu on the left scan down past Favourites to find your name, and right-click on it.
In the menu that appears, select “Add shared folder...”
In the prompt that comes up, start typing the full name of the mailbox you wish to open, not the email address. If the name does not autofill, type it in and select “search contacts and directory” to find the mailbox.
Once you have selected the correct mailbox, click Add to add that mailbox to your folder menu.
You will then see the mailbox listed in the left hand panel below your mailbox