DIY: Cure Outlook .pst and .ost woes

In response to a TechRepublic member question, Jack Wallen reveals a couple of troubleshooting steps he takes when Outlook is muddying the waters of the powerful .pst and .ost files.

Read my answer to an anonymous TechRepublic reader's question, and then please post additional tips for the member in the discussion.

Q: One of my client's Outlook is acting strangely and I cannot pinpoint the problem. What can be done without costing the client too much money and wasting too much of my precious time?

A: That is a great question, and one that we deal with quite a lot. Outlook is an incredibly complex application that can stump even the best of administrators. I always like to start with the simple and (almost) obvious first — the .ost and/or the .pst file.

  • .pst: This is the file that resides on either the Exchange server or the user's local machine and keeps the user's data.
  • .ost: This is the offline file that Exchange uses to sync a user's data. This file resides on the user's local machine.

It's very important to make sure these file sizes haven't gotten out of hand. Although Microsoft states that the file size limit of a .pst file is 20 Gigs, we have found that anything above four Gigs can start causing issues.

As for the troubleshooting, what you do will depend upon what the user has. Let's assume the user's machine has an .ost file and no .pst file. If that's the case, this is what I do:

  1. Close Outlook.
  2. Locate the .ost file.
  3. Rename the .ost file.
  4. Fire up Outlook and let it re-sync.

In these types of setups, I usually find that this process does a world of good. If Outlook still has issues, it's time to look at the .pst file and take advantage of a tool that Microsoft includes with Windows called scanpst.exe. Here's what you need to do (note: this process can take quite some time):

  1. Close Outlook.
  2. Do a search for scanpst.exe and then open the containing folder.
  3. Run the scanpst.exe application.
  4. Use the tool to open the .pst file in question and scan for errors and repair them.

Hopefully, the tool will find and fix any errors in the file, and your user will have Outlook back in perfect working order.

Ask Jack: If you have a DIY question, email it to me, and I'll do my best to answer it. (Read guidelines about submitting DIY questions.)


Jack Wallen is an award-winning writer for TechRepublic and He’s an avid promoter of open source and the voice of The Android Expert. For more news about Jack Wallen, visit his website

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