How to add an old .pst or archive .pst file to Outlook 2010
Outlook emails may be saved in .pst files. For example, you may have a file called archive.pst or something similar, that you want to get into Outlook 2010.
Click on File, Info, Account Settings then Account Settings, as in the image below.
Click on the Data Files tab, then on Add. Make sure that Outlook data file(.pst) is highlighted and click on OK.
Browse to your .pst file and click on OK.
You should now find your mail in Outlook, listed below your email folders, as shown below.