Here’s my take on this.
Recovering emails from the server side in Outlook, even after emptying the “Deleted Items” folder, is often possible, but it depends heavily on your organization’s IT policies. Most business Outlook accounts (using Microsoft Exchange) have a secondary recovery feature.
If you go to your ‘Deleted Items’ folder, you should see an option like ‘Recover items recently deleted from this folder.’ This accesses a ‘Recoverable Items’ folder on the server where emails are held for a set retention period—usually 14 to 30 days—before being permanently purged.
So yes, your boss’s email might still be there if you act within that timeframe. If that feature doesn’t work, the company’s IT department may have more advanced recovery tools at their disposal.