Reduce the File Size of Outlook Data

Reducing the file size of Outlook data files (.PST or .OST) can improve performance and free up storage space. Here are several methods to achieve this.

1. Archive Old Emails

• Open Outlook and go to File → Options → Advanced
• Click AutoArchive Settings and configure it to move old emails to an archive file
• Alternatively, manually move older emails to a separate PST file via File → Open & Export → Open Outlook Data File

2. Delete Unnecessary Emails and Attachments

• Sort emails by size (View → Arrange By → Size) and delete large ones
• Remove attachments from emails:
  • Open the email, right-click the attachment, and select Remove Attachment
  • Save the attachment to your computer before deleting it if needed

3. Empty Deleted Items and Junk Folders

• Right-click Deleted Items or Junk Email folder and select Empty Folder
• Ensure you permanently delete them (Shift + Delete) for space to be reclaimed

4. Compact the Outlook Data File

After deleting emails, Outlook doesn't immediately reduce the file size. You need to compact the data file:

1. For PST or OST Files:
   • Go to File → Account Settings → Data Files
   • Select the PST or OST file and click Settings
   • Click Compact Now

5. Reduce Sync Settings (For OST Files)

If you're using an Exchange, Microsoft 365, or IMAP account, you can limit the amount of data stored in the OST file:

1. Go to File → Account Settings → Account Name & Sync Settings
2. Adjust the slider under Mail to keep offline to a shorter duration (e.g., 3 months instead of all emails)
3. Restart Outlook

6. Split Large PST Files

If your PST file is too large:

• Use Move to Folder to transfer old emails to a new PST file (File → New Outlook Data File)
• Keep separate PST files for different years or projects

7. Disable Unused Add-ins

Too many add-ins can slow down Outlook and increase the data file size:

• Go to File → Options → Add-ins
• Disable unnecessary add-ins

8. Use Online Archive (For Microsoft 365 Users)

If you have a Microsoft 365 account, enable Online Archive to offload old emails to the cloud without affecting the local OST file.

9. Recreate OST File (For Outlook with Exchange or IMAP)

If your OST file is too large or corrupted:

1. Close Outlook
2. Locate the OST file at: C:\Users\YourUsername\AppData\Local\Microsoft\Outlook
3. Delete or rename the OST file
4. Restart Outlook — Outlook will recreate the OST file by syncing with the server