Adding an Additional Mailbox in Outlook on the Web

If a user has access to an additional/shared mailbox they can add it to their Office365 web mail. 
 Step-by-step guide 
 
 
 Sign in to your account in Outlook on the web. 
 
 
 For Exchange Online mailboxes, right-click  Folders  in the left navigation pane, and then choose  Add shared folder or mailbox then Add shared folder or mailbox . 
 
 
 
 In the  Add shared folder dialog box, type the name of the shared mailbox you are a member of, such as info@pbr.org.au.