How to add users to a shared mailbox in Office 365?

Step 1: Sign into your Office admin account via https://portal.office.com

Step 2: Navigate to Exchange admin center.

Step 3: On the left pane, scroll down and click More features.

Step 4: Click open under Permissions.

Step 5: Click Recipients on the left pane.

Step 6: Switch to the Shared tab.

Step 7: Double-click on a mailbox and switch to the email address tab.

Step 8: Click on the add(+) icon.

Step 9: Select email address type, enter the email address in respective box and click OK.