Outlook: Adding a Shared Mailbox (Outlook Web App + New Outlook) What will be covered: How to open a shared mailbox How to set a shared folder / Mailbox  1. Open Outlook Web App Navigate to the Office 365 portal ( https://outlook.office365.com ) and log in with your credentials. 2. Open Shared Mailbox Click on your profile picture or initials in the top-right corner, Select Open another mailbox . Lastly Enter the email address of the shared mailbox and click Open. The shared mailbox will open in a new tab. 3. Add Shared Mailbox to Folder List Right-click Folders in the left navigation pane.  Right click the Folders and Select Add shared folder. Enter the email address of the shared mailbox and click Add .