How to compact an Outlook PST file

After you remove messages or attachments from your mailbox, the PST file size will not necessarily reduce by itself. In order to shrink the size of the PST file, you need to compact it.

To compact a PST file:

  • Right click on the top-most folder of your PST. (It is usually called “Personal Folders”, but may also have a different name).
  • Select “Properties for…”
  • Click “Advanced”
  • Click “Compact Now”

See [permalink href=”14″]more tips on improving Outlook performance and stability[/permalink].

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    10 Responses to “How to compact an Outlook PST file”


    • I have tried the “Compact now” function but the message is displayed for only 2 seconds and the pst itself is not compacted. Any clues – my pst is 636MB?

    • That likely means you do not have any “empty” space in your PST. All 636 MB are taken up by messages and attachments. Please do not hesitate to contact us with further questions using this link –
      http://www.TechHit.com/contact.html

    • I’m having the same problem with my Outlook 2007. I have cleared all the Deleted Items and gotten rid of any emails I do not need. I have deleted any large emails which have Attachments.

      The Folder Sizes in my Outlook are about 12MB. But my PST file is 60MB.

      I have compacted many times, but the Compact Now function only opens for a second or two before completing. It used to go down to 20MB but now it does not seem to go down from 60MB.

      (Please don’t teach me to Compact a PST file. I know how to do it and I have been using this function for many years)

      The problem now is that the file does not seem to want to go down in size to what the folders claim is being used.

      • PST file size will always be significantly larger than what is reported by “Folder size”. And as far as PST files go, 60MB is relatively small, so I do not think you should be concerned about this.

        If you do suspect that there are issues with your PST file, you could run the scanpst tool on it. Please see this page for instructions – http://support.microsoft.com/kb/287497

        If you would like to experiment further, you could create a brand new PST file and copy all messages and folders into the new PST. To create a new PST file, select
        “File->New->Outlook Data File” menu command in the main Outlook window.

    • Ok guys, I figured out why my PST file was not reducing in size back to 20MB. I ran the SCANPST application that comes with Office to scan and fix any errors in my PST file. After this was done I was able to compact the file down again. Now I have a 20MB PST file instead of the 60MB.

      So here is the Tip, Run SCANPST.EXE to see if there are some errors with your PST file.

    • Thanks, Wobble!

      This is just what I have been looking for. I had the same issue of the compact not reducing the file even after I ad archive over 1.2g of data. After I ran scanpst (which is in Program Files\Microsoft\Office12), and then compacted, I reduced my pst from 2.7g to 1.3g! Hooray!

    • I’ve tried doing a scanpst and then tried to compact my pst file, but to no avail. It just does not reduce the file size while I know that the actual size of the files in the pst is a lot less than the physical file size.
      scanpst does not bring up any errors either.
      Any suggestions?

    • Hi all.
      I just met the same problem and the situations is as folowing:
      There is a pst file on the share. Once it grew up I checked it and realized that the folder size told by outlook are 340 MB while it takes over 600 Mb on the server. I followed all instructions above and after file was repaired by ScanPST utility and compacted in outlook it became about 380 Mb. But then this file was in use for a one day and now is taken over 500 Mb while outlook talks about 350 MB. Are there any ideas?

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