Outlook Add-in: Expose shared mailbox properties on the mailbox object in a multi-select scenario

We require a reliable method to retrieve the properties of a shared mailbox in an OWA client when multiple emails are selected.

Currently, when multiple emails are selected, Office.context.mailbox.item becomes null, which blocks access to the shared mailbox identity via Office.context.mailbox.item.getSharedPropertiesAsync() - the only available retrieval method.

The issue with multi-select in a shared mailbox is captured and elaborated on in great detail over here