To do this you must be in the Outlook Desktop App. It is also important to note that this is only relevant if the email was deleted less than 30 days prior to retrieval.
1. Click the 'Folder' tab and then click recover deleted items.
2. You will then be given a list of permanently deleted items from your email. Find the email that you require to recover.
3. Select items that you would like to recover (holding Ctrl when selecting if multiple) and then click OK, ensuring that 'Restore Selected Items' is selected.