How to Compact a PST File in Outlook

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When you delete an email in Outlook, it goes to the trash, i.e. the Deleted Items folder.  When you empty the Deleted Items folder, all the deleted messages disappear—but they are still in your PST file.

While Outlook periodically reclaims that wasted space in the background, you can manually initiate the process, too. This makes good sense after you have emptied the Deleted Items folder for the first time after a lot of spam, or if you have just moved a year's worth of mail to your archive PST, for example.

Compact a PST File to Reduce Its Size in Outlook

To manually start reclaiming wasted space in an Outlook PST file:

  • Select File | Data File Management... from the menu in Outlook.
  • Highlight the desired PST file.
  • Click Settings...
  • Now click Compact Now.