1. In Outlook, click on File > Open & Export.
   
   
2. Now click Import / Export.
   
   
3. Select Export to a File and click Next.
   
   
4. Now select Outlook data file (.pst) and click Next.
   
   
5. Select the uppermost folder in your mailbox tree, tick Include sub-folders and click Next.
   
   
6. Now choose a location on your PC to save the backup file, and click Finish.