Add Mail Rules to Shared Mailboxes in Outlook Go to https://outlook.com. Click "Sign In" on the top right using your full email address. Once you are at the mailbox screen, click on your profile icon on the top right and select "Open another mailbox". Enter the address of the shared mailbox you would like to open and click "Open". Once the shared mailbox is open, click the settings/gear icon on the top right. Under Mail > Rules, select "Add a new rule".