Here is a link to a post about backing up data files in Outlook:
http://www.thetraininglady.com/backu...-file-outlook/

This will show how to find the PST file and then add it to your backup routine.
If you make a copy of the entire PST file you can obviously save it to a separate location on your computer or a USB drive. If you want to open the file later to access just one email within it, and ensure you do not affect your current email folders, you do this through the File tab and choose Open & Export, then click Open Outlook Data File. Navigate to the file location and select it and click Open. The file SHOULD open as a separate PST file within your email profile and allow you to browse through it and open any of the content. Once you are finished with it simply right mouse click on the Personal Folders listed in the Folder pane on the left and click Close Folders.

Let me know if you are still having issues or need further information.