1:) Is it still in the Deleted Items Folder?
If so - Done.
If Not Will depend on how you connect to the mail server.
2:) Do you have webmail access?
If so - Check it.
If you have to contact IT, take the rolled eyes and tuts you deserve like a man and be nice, or the random delete punishment fairy might pay you a visit.
Selected your deleted items folder. Now click on Tools and an option called ‘Recover Deleted items’ should have appeared… Click on this and it will start finding emails that were long gone
Edit: woops just saw duncmac’s link was pretty much the same thing…
That is also time limited, it is usually set to 30 or 60 days. If it is not in your deleted items, then it will have to be recovered from tapes. Not a simple task, and to be honest unless it is business critical then the request is likely to be refused.