Managing Large Outlook OST Files

Understanding OST Files

OST (Offline Storage Table) files are used by Microsoft Outlook to store a synchronized copy of your mailbox data. Over time, these files can grow significantly in size, affecting performance and storage space.

Solutions for Reducing OST File Size

1. Delete Unnecessary Emails

One of the main reasons that an Outlook OST file can increase in size is because it contains a large number of emails that are no longer needed. To reduce the size of the OST file:

  • Use the search function in Outlook to locate and delete emails that are no longer needed
  • Focus on emails that are more than a certain age
  • Remove emails from specific senders
  • Clear out large attachments

2. Compact the OST File

Outlook includes a feature called “Compact Now” that can be used to compact the OST file and reduce its size. To compact the OST file:

  1. Go to the File menu in Outlook
  2. Select the “Account Settings” option
  3. In the Account Settings window, select the email account
  4. Click on the “Change” button
  5. In the Change Account window, click on the “More Settings” button
  6. Go to the Advanced tab
  7. Click on the “Offline Folder File Settings” button
  8. Click on the “Compact Now” button

3. Repair the OST File

If the OST file is corrupted or damaged, it can cause the file to increase in size. To repair the OST file:

  1. Locate the Inbox Repair Tool (Scanpst.exe) in your Outlook installation folder
    • Usually located at: C:\Program Files\Microsoft Office\root\Office16 for Outlook 2016
  2. Double-click on the file to launch the Inbox Repair Tool
  3. Follow the prompts to repair the OST file

4. Archive Old Emails

If you have a large number of old emails that you want to keep but don’t need to access regularly:

  • Use Outlook’s built-in archiving feature
  • Set up automatic archiving rules
  • Store archives in a separate location
  • Consider using PST files for long-term storage