Below is the procedure to import a .pst file.
1. Open Outlook
2. From the menu, choose “File” > “Import and export”
3. Select "Import from another program or file", click Next
4. Select "Personal Folder File (.pst)", click Next
5. Select the PST file and click Next. The default name and location of the PST file is: C:\Documents and Settings\"YourLogin"\Application Data\Microsoft\Outlook\outlook.pst. If you have used previously specified a non-default locatioin for your PST file, you have to specify the PST file from that alternate location.
6. Under “Select the folder to import from:” ensure that “Personal Folders” is selected.
7. Check the “Include SubFolders” box.
8. Select “Import items into the same folder in:” and “” should be selected from the dropdown listbox (normally the default selection).
9. Click Finish.
10. The import process will start and may take a few moments depending on the amount of data to be imported.
Note: The information needed to import Outlook Post Office files (.pst) can also be found in the extensive online help files contained within the Exchange Online Control Panel.