Here is the procedure to import an existing PST File in Outlook 2010
. Open Outlook
2. Go to File
3. Click Open
4. Click on Import.
5. Select Import from another program or file and click on Next.
6. Select Outlook Data File (.pst) and then click on Next.
7. Click on Browse.
8. Locate the pst file that you wish to Import. Click on Open.
9. Click on Next.
10. Click on Finish.
11. This process might take time based on the amount of data. You can check the progress in your Progress Bar. When it closes, the files will be imported in the mailbox.