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Outlook: Solve “The file username.ost is in use and cannot be accessed” Error

By Mitch Bartlett 14 Comments

Microsoft Outlook 2016 crashed on me today. When I tried to launch it again, I received an error that said:

Outlook Data File – The file C:\Users\user name\AppData\Local\Microsoft\user name\username.ost is in use and cannot be accessed. Close any application that is using this file, and then try again. You might need to restart your computer.

 Restarting my computer was not an option at the time. Here’s how you can solve the issue.

Fix 1 – Kill All Outlook Related Processes

  1. Right-click the task bar and select “Task Manager“, or press CTRL + ALT + Delete, then choose “Task Manager“.
  2. Select the “Processes” tab.
  3. Look for anything named “Communicator“, “Lync“, “ucmapi” or “Outlook“. If you find any items related to these, select it, then select the “End task” button.

Fix 2 – Restart Computer

Rather than spend all day trying to figure out the process that is hogging the file, try just doing a simple computer restart. Select “Start” > “Restart“.


Fix 3 – Disable Cached Exchange Mode

  1. Close Outlook.
  2. Open “Control Panel” and select “Mail“.
  3. Select the “Email Accounts” button.
  4. Choose the “Email” tab.
  5. Highlight the email address giving you the warning (email.ost), then select “Change“.
  6. Uncheck “Use Cached Exchanged Mode“.
  7. Select “Next” then “Finish“.

Now attempt to launch Outlook again. Hopefully, it works fine now. This is more of a workaround than a fix, as it switches to where you are using Outlook direct from the server. This may cause speed issues. If you have problems with Cached Exchanged Mode disabled, try enabling it again at a later time by rechecking the “Use Cached Exchanged Mode” box in step 6 above.

If neither of these fixes work, you might have another computer or program grabbing the OST file. Makes sure anything that uses Outlook is completely closed on any workstation that may interface with Outlook.

Thanks to Alix Jimenez for Fix 3.

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Filed Under: Software Tagged With: Outlook 2013, Outlook 2016

Reader Interactions

Comments

  1. Deven Malik says

    January 27, 2022 at 3:23 am

    You can also try out the steps mentioned below to resolve the issue

    https://www.magustools.com/blog/how-to/how-to-fix-file-username-ost-is-in-use-cannot-be-accessed-error/

  2. PK says

    December 13, 2021 at 9:10 am

    Appears that Cortana was holding onto the ost file too long.

  3. Shedrach Oshofisan says

    August 6, 2021 at 7:29 am

    Thanks for this workaround fix. the third fix work for resolving the present issue.

  4. Aidan says

    May 31, 2021 at 11:45 pm

    Closing WebEx stopped this error appearing.

  5. John Biard says

    March 24, 2021 at 2:44 pm

    Like several others, method 3 worked for me. Thanks again

  6. James says

    January 22, 2021 at 7:25 am

    Closing Skype worked for me

  7. Madhu Ammu says

    May 2, 2020 at 8:02 am

    Thank you very much…
    Your recommended tip helped me to resolve the outlook issue that i have been facing for the last one month :-)

  8. Narasimha Rao Taduri says

    April 28, 2020 at 1:21 am

    Thank you so much. You saved my time. Method 3 worked for me

  9. M Ray says

    February 7, 2020 at 3:02 pm

    Fix 3 worked great!! Thanks

  10. Michael Wigle says

    February 27, 2019 at 1:44 pm

    Fix number 3 fixed a problem where e-mail got stuck in the outbox and the progress details complained about not being able to access the outlook data file. Appreciate finding your post.

  11. Bill K kapri says

    October 18, 2018 at 9:38 am

    Brah thank god youre a life saver

  12. Edmund Esterbauer says

    September 6, 2018 at 9:58 pm

    I removed the .ost account by deleting it and reinstalled the email account and it is now working. Thanks for the help of getting there.

  13. Muhammad Asim says

    September 6, 2018 at 4:09 am

    Thanks Mitch, method 1 worked like charm. It seems one of the reasons why OST file gets engaged can be related to updates on machine and/or reboot. This is what i last did yesterday and today outlook would not start. Many Thanks!

  14. Erwin Parker says

    August 29, 2018 at 12:02 am

    Closing Skype for Business before trying to open Outlook again does the job!

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Who’s Behind Technipages?

Baby and Daddy My name is Mitch Bartlett. I've been working in technology for over 20 years in a wide range of tech jobs from Tech Support to Software Testing. I started this site as a technical guide for myself and it has grown into what I hope is a useful reference for all.

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