Outlook.pst was Not Cleanly Closed By The Last Program – Solved

Written By Ashwani Tiwari
Anuraag Singh
Approved By Anuraag Singh
Published On October 4th, 2023
Reading Time 6 Minutes Reading

Outlook is the most popular desktop-based email client used by people these days. It has file extension called PST that is used to save major data like contacts, calendar, emails etc. But using Outlook there are plenty of issues people face at one point or the other. One such issue is Microsoft Outlook 2013, 2016 won’t open because Outlook.pst was not cleanly closed by the last program that used it.

There are many reasons for this error to occur, one of them is large PST file size. This message does not access Outlook but it definitely increases the accessibility time of Outlook. In this article we will discuss the ways to fix the Outlook data file .pst was not cleanly closed by the last program that used it.

Let us understand the topic well with the help of a query”

“Hello! I have been using Microsoft Outlook for quite some time and recently I have upgraded my computer to Windows 10 and Office 2010 to 2016. But when I am starting my Outlook 2016 it is showing error message Cannot start Microsoft Outlook. What I understood was Outlook 2016 PST was not cleanly closed by the last program. Could someone tell me how to fix this problem as I have many important official files saved in Outlook? Thanks in advance.”

Reasons for – Outlook.pst was not Cleanly Closed by the Last Program

There are various reasons that can result in Outlook 2013, 2016 won’t open because Outlook.pst file was not cleanly closed by the last program that used it. Few are listed below:

  • Shut Down: Before Outlook was closed, the Windows was shut down, this causes the occurrence of an error, PST file was not cleanly closed issue.
  • External Software: In case of third-party tool trying to access Outlook data or the add-ins which close the data improperly may result in the occurrence of the error.
  • Virus Attack: Virus attack on Outlook data can also result in the occurrence of error message
  • Corruption: The data file cannot be opened if the Microsoft Outlook crashes because of corruption. It further shows the error message i.e. “Outlook.pst was not cleanly closed by the last program”

The Sequence Of Starting the Outlook with Error Message

  • Start Outlook
  • An error message occurs i.e. the Outlook data file .pst was not cleanly closed by the last program that used it. The file is being checked in order to find problems.
  • A warning message is displayed that states “Performance might be affected while checking in the progress”. After some time the message comes “Data file check complete”
  • Email can be opened and accessed along with other Outlook components.

Also Read: How to fix Outlook error PST file cannot be found issue manually?

Assessment of Problem

The user has to first assess the problem of the occurrence of the error. If the Outlook is taking too long to respond there could be a reason like the size of Outlook data file is huge. Sometimes the size of PST file becomes too large which results in improper opening and accessing of Outlook files. There are chances of corruption of PST data file since Outlook.pst was not cleanly closed by the last program. In this regard, we will take the help of manual method in form of reducing the size of PST file or repair PST using ScanPST.exe file.

Method-1: Use Inbuilt Utility  ScanPST.exe File

If archiving and compacting method does not solve the problem of error. Then the user can fix miner issues of PST file using ScanPST.exe file. Follow the instructions:

  • By exiting Outlook location, ScanPST.exe to be started manually. There is a variation in the location of inbuilt utility with respect to Outlook versions and different Windows OS. Locate Inbox Repair Tool or ScanPST.exe.
  • After that Browse the PST which is to be repair, there should be the presence of extension .pst.
  • Then click on Options and also provide Scan Log Option.
  • Then Start button to be clicked. If some errors are detected then the file prompts to start the repair process.
  • In order to avoid data loss, the backup file is created. The user can save the file in the preferred location.
  • Lastly, click on Repair button and Outlook to be started using the profile with PST file.

Method-2: Use Professional Tool to Secure Data

The PST Repair Tool can be used to fix PST corruption which is the reason for many Outlook the error “Outlook.pst was not cleanly closed by the last program”. The application repair corrupted PST files with minor and major corruptions of personal folder file.

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Method-3: Reduction in Size of PST File

There may be an error due to the oversized PST file. In that case, the size of the PST file has to be reduced. This can be done with archiving and compacting process.

  • Begin Outlook, move to File Tab. Click Info.
  • Click the Cleanup tools. Afterward, Click on Archive.
  • In the archive dialog box following steps have to be performed:
  1. Start Archive this folder and subfolders option
  2. Select the PST file to be archived from the list of folders
  3. Specify a date for items to be archived by choosing from the drop-down list with the name Archive items older than.
  4. Destination path and archive into new PST file to be selected as the user might be archiving a large number of email messages
  5. Split large PST file and save at a preferred location


While using Microsoft Outlook it is very common for the user to face error like Outlook.pst was not cleanly closed by the last program that used it. There are various reasons responsible for this PST file error but the major reason for such an error is the too big size of PST. There are manual methods given that can reduce the size of PST file or repair PST with ScanPST.exe. Also, there is another method to recover errors of MS Outlook PST using the PST fix utility discussed above.