You can now add a shared mailbox that you already have permission to, and access it via Outlook Mobile for iOS and Android,
IIf you already have full access to a shared mailbox, you have the ability to change the 'Out of Office' automatic message on that account.
If you have been granted access to another mailbox, either another persons mailbox or a shared email account, use these steps to add that account to your Outlook for Mac.
If you occasionally send mail from a Shared Mailbox, you can quickly change your email signature in the desktop version of Outlook.