You must have been given permission to access the additional mailbox before it can be added to Outlook.
To request permission to the mailbox, please have the owner of the account contact us.
Sign in with your UCCS email address and password
Once logged in, click on your name in the top-right corner to open the Settings pane.
Click Open another mailbox…
Type in the name of the exception account you would like to access:
Click Open to open the exception account's mailbox: