Note: There are different type of File Extension available in Microsoft Outlook some are below
.pst ( Personal Folders)
It contain mails, contacts, calendar requests and it is available on locally system. It has a 2GB file size limit. its default location is C:\Documents and Settings\<username>\ Local Settings\Application Data\Microsoft\Outlook in XP, where as in Vista/7/8 the Location is C:\Users\<user>\AppData\Local\Microsoft\Outlook.