Open the Apple Mail app.

Click 'Mail' on the Mac system bar at the top of the screen and select 'Preferences' from the drop-down menu.

Click on the '+' symbol at the bottom left of the pop-up window and select 'Other Mail Account'. Click 'Continue'.

Enter name and email address of the shared mailbox you wish to add, and your UIS Password. Click 'Sign In'.

Fill out the pop-up window as follows:

Email Address: [the shared mailbox email address]
Username: [Your CRSid]@cam.ac.uk\[email address of shared mailbox]
Password: [Your UIS Password]

Account Type: [Leave as IMAP]
Incoming Mail Server: outlook.office365.com
Outgoing Mail Server: smtp.office365.com

Choose if you want to have Notes included with the Mail account and click 'Done'. Close the 'Accounts' dialogue box.

Your shared mailbox should now appear in the list of inboxes in Apple Mail.