Outlook Desktop
Adding a shared mailbox to Outlook for Windows - Instructions for O365 Shared Mailboxes
Adding a shared mailbox to Outlook for Windows - Instructions for Connect (on-prem) Shared Mailboxes
Adding a shared mailbox to Outlook for Mac - Instructions for Connect Shared Mailboxes https://uwaterloo.atlassian.net/wiki/spaces/ISTKB/pages/1854013815
Outlook Web Version
Sign in to your account in Outlook on the web. (https://outlook.office.com/)
On the Outlook on the web navigation bar, click the person “image” at the top right. A list appears.
Click Open another mailbox.
Type the email address of the shared mailbox, and then click Open.
Another Outlook on the web session opens in a separate window, allowing access to the other mailbox.
You may be required to log in again. Make sure you use your own username and password