File format (.pst)
From Conservapedia
The file extension .pst is a type of file format used in the software program Microsoft Outlook to maintain email files other than in a users active mailbox. .Pst files have a limitation that they are not able to be opened by more than one user at a time without additional software. It is possible however to copy .pst files to numerous users as long as the .pst is not in use by Outlook.
