Mutliple OST files generated by Outlook with FSLogix


We recently started having issues with FSLogix and Outlook and hope someone has seen this before and can offer some assistance.

We have been using FSLogix Office Containers in our VDI environment for a couple of years now without any major issues. However, we recently started having issues with Outlook creating a new OST file every time a user launches Outlook in a new session. This is mainly happening to new users in the VDI environment, and I confirmed this by deleting my profile and logging into VDI as a new user.

If I log into a VDI session and launch Outlook, it will start and say "Preparing Outlook for first use." every time I log in.

  • If I mount my VHDX file and browse to the ODFC folder, (or go to %localappdata%\Microsoft\Outlook in the VDI session) I can see multiple OST files of the same size on the drive.
  • I have checked the registry keys for FSLogix in the VDI session and can see they are being mapped correctly.
  • I can put the path of my FSLogix container in file explorer and it maps without issue
  • FSLogix logs do not show any errors, and redirections are mapping correctly.
  • We are also seeing similar issues with OneDrive where it requires a login and re-syncs every time it is started.



  • Horizon 7.13.1
  • DEM 9.11
  • FSLogix
  • Windows 10 21H2
  • Office 2019 (Outlook with cached mode enabled)

Recent Upgrades

  • Windows 21H2 (Updated to latest patch levels)
    MS Office 2019 (Latest Patch levels)
  • SentinelOne
  • FSLogix latest drivers (to try to resolve this issue)


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2 Replies
Hot Shot
Hot Shot

Do you have a GPO for the Exchange setting?

Navigate to:

User Configuration -> Policies -> Administrative Templates -> Microsoft Outlook 2016 -> Account Settings -> Exchange

And set “Automatically configure profile based on Active Directory Primary SMTP address” to Enabled.

“One time Only”. Using the One time Only will not try to apply the configuration on all subsequent Outlook runs.

Not sur eif the one time will help.

I looked at my %localappdata%\Microsoft\Outlook and see 2 files the same size with different extensions. username.nst and username.ost. You have the same?

Please mark helpful or correct if my answer resolved your issue.
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Thanks for replying and the suggestion, but for some reason it stopped happening shortly after posting, and the issue has not returned, but I'm not exactly sure why. And I cannot make it reoccur.

FWIW, when the issue was present, I had 6 different ost/nst files in my %localappdata%\Microsoft\Outlook folder. A new one would get created every time I launched Outlook at a new login. All had the same filename with the traditional Windows (1), (2), (3) at the end of the filename.

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