PST Files and OST files

A lot of people seem to be confused by Outlook files so let me try and explain the differences.

PST Files -

These are Outlook data files which hold all your Outlook data from Contacts / Tasks /Calendar / Notes / Attachments to all your email including ALL sub folders.

By Default they are stored in the following location

Windows XP and before
C:\Documents and Settings\username\Local Settings\Application Data\Microsoft\Outlook\
Windows Vista
C:\Users\Username\AppData\Local\Microsoft\Outlook\

Where Username is your profile name

There are 2 types of PST files
Outlook 2002 and Before and Outlook 2003 / 2007.

Outlook 2002 and Before: These have a limit of 2GB in size.  However they will start to become corrupt after 1.7GB If the PST file becomes corrupt then it will need to be repaired.

Outlook 2003 / 2007 : These have a limit of 20GB.  However whilst i have never seen a corrupt one i would not want to try and recover a 20GB PST as it would take many hours to recover so i would never suggest having a PST over 3-4GB.

If you use POPMail then you all your email is downloaded and stored into a PST file so you should backup the PST file as its your only copy of the email in Outlook.

If you use Exchange mail (Corporate email on Outlook) then only email you store in an Archive is stored in a PST file.

PST files should not be deleted unless you have checked the content is not needed as if cannot be recovered.

OST Files -

These hold an offline COPY of your Exchange Mailbox.  With Exchange email your Mailbox which contains Contacts / Tasks / Notes / Calendar / Email / Attachments resides on a Server but to enable yourself to view your mailbox offline you can setup and Offline Store (OST file).  This is a copy of your mailbox which synchronises changes in your mailbox to your OST File when you connect.   You can delete your OST and recreate it as its only a copy of your Mailbox.

OST Files are kept in the same location as PST files.

Windows XP and before
C:\Documents and Settings\username\Local Settings\Application Data\Microsoft\Outlook\
Windows Vista
C:\Users\Username\AppData\Local\Microsoft\Outlook\

Where Username is your profile name


You can change the location where PST and OST files are stored.