How to Fix Outlook PST File Size Not Reducing After Deleting Emails Issue

Jackson Strong | December 31st, 2025 | Data Backup

Do you have a big PST file? We love large PST files, which consist of all of our data in one place. But the real issue comes when Outlook PST file size not reducing after deleting emails. Well, we love finding out what makes PST files big and all the ways that can be used to make them small again. So, today we are going to show you how to shrink PST file after deleting emails.

Starting with why…..

Before we dive in, it’s worth noting that there are many reasons why Outlook data file size not reducing after deleting emails. So, it’s important to start with a clear understanding of the reasons behind this issue.

Let’s get started!

Why Outlook PST File Size Not Reducing After Deleting Emails?

  • PST File Structure: PST file is designed in such a way that it can only grow, not shrink, even after deleting emails.
  • Corruption Issue: If your PST file is corrupted, then it can prevent Outlook from freeing unused space.
  • Unused Space Remains: When you delete emails from PST file, the space remains unused, which may prevent your PST file size not reducing even after deleting emails.
  • Large Email Attachments: Emails with large attachments can also create a hurdle to not to reduce PST file size. Even after email deletion, it stays inside file until you compact it.
  • PST File Fragmentation: Over time, PST files become fragmented, which allows Outlook to use its space again.

Now, let’s go through each method step by step and help you find out the best one as per your needs and requirements.

How to Shrink a PST File After Deleting Emails?

Helpfully, there are some methods available that you can try to check to reduce PST file size. All the solutions are tried and tested professionally, so you can trust them to implement in your own way.

#1. Compact PST File

Try to compact the PST file first, which will remove its unused space and reduce the file size.

  1. Run the Open Outlook application and click the File tab.
  2. Next, tap on the Account Settings >> Account Settings.
  3. Select data files as per your need.
  4. Choose the PST file and click Settings.
  5. Click the Compact Now button.

Wait for a while, it will take time as per PST file size.

#2. Archive Old Emails

If the above method doesn’t work for you, next try to archive old emails, which will move older emails out of the main PST file into a separate archive file. This reduces the active PST file size and improves Outlook performance.

  1. Run the Outlook application and click on the File tab.
  2. Next, tap on Tools >> Clean up Old items option.
  3. Select the required folders to archive.
  4. Also, choose the needed date to archive old emails.
  5. Choose the location where you want to save archive PST file.
  6. Now, Outlook will move old emails to archive file.

Note: It will take time, as per your mailbox size.

#3. Remove Attachments

Here, we can remove attachments from PST emails instead of deleting the entire message. This helps reduce PST file growth while keeping important emails secure.

  1. Run the Microsoft Outlook application on your computer.
  2. Click the File tab, then choose Tools >> Mailbox Cleanup.
  3. Click Find items larger than and enter a size. Tap the Find.
  4. This shows emails that are taking up the most space.
  5. Now, open an email with a large attachment.
  6. Right-click the attachment and select the Save As option.
  7. Save it to a folder on your system or cloud storage
  8. Right-click on the attachment again and tap remove attachment.
  9. Save the email.
  10. The email stays, but the attachment is removed.

Now, repeat for other large emails to see if your Outlook PST file size not reducing after deleting emails issue resolves or not.

Still Having Trouble? Try a Practical Solution Now!

If none of these methods work for you to shrink a PST file after deleting emails, then it can be due to major issues. Such as PST file is very large, it is fragmented, it has strict limits, due to PST file corruption issues, and many more. In these cases, Outlook’s built-in tools are not enough; you need an effective tool to solve any issues immediately. In our suggestion, we will recommend that you try the Advik PST Splitter Tool. It can help you manage large PST files and deal with issues like PST file size not decreasing after deleting emails. You can use this tool to export PST data into smaller files of various sizes without compromising the data integrity.

Click on the Free download button and check how it can be helpful for you.

Conclusion

Now, we have reached the end of this blog. We hope that we were able to help deal with the issue when Outlook PST file size not reducing after deleting emails. While exploring all the reasons and fixes, we understood that deleting emails from PST file is not merely required to reduce its size. You have to take various necessary measures to shrink PST file. You can try all the manual fixes, and if it doesn’t work for you, an alternate solution is also given to solve it in a better way.

Must read the complete blog to make a wise decision.