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We have somebody who uses Outlook 2016, and we joined his computer to an active directory. For this, we used the ProfWiz domain migration tool to convert his local profile into a domain profile, while retaining all data. We have good experiences with this tool, and it worked flawlessly many times before.

However, for this user, we get the dreaded message similar to:

Cannot expand the folder. The set of folders cannot be opened. You must connect to Microsoft Exchange with the current profile before you can synchronize your folders with your Outlook data file (.ost).

(The German original is actually:)

Microsoft Outlook kann nicht gestartet werden. Das Outlook-Fenster kann nicht geöffnet werden. Diese Ordnergruppe kann nicht geöffnet werden. Auf die Datei 'D:\path\to\john.doe@company.com.ost' konnte nicht zugegriffen werden. Die Verbindung mit Microsoft Exchange muss mindestens einmal hergestellt worden sein, damit Sie ihre Outlook-Datendatei (OST| verwenden können.

We are using Office365 for Business (no local Exchange server). The only thing unusual about this user is that he has a huge .ost file (50 GB), and he thus moved it to another partition. We guess that it did not get the correct permissions when converting the PC, however this does not seem to be the case. Even after granting permissions to the new (domain) user to the file, he cannot start outlook.

There is a lot of data that is stored offline in the profile that we don't want to loose, so deleting the .ost and starting over is no option.

I cannot get into Outlook when loading the .ost to enter the password, because without logging in I cannot open the .ost... I also exhausted every option in the "Mail" control panel applet, I think.

Is there a way to fix this situation? Would undoing the domain conversion help? Could we delete everything, and then import the data from the .ost?

jdm
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  • An OST is a cached copy of the Exchange/O365 mailbox. Is it mail not moved to O365? If it from is O365 you loose nothing, as the Outlook client will just recache at next login – yagmoth555 Mar 07 '19 at 11:33
  • Like mentioned the OST file is a cache. All the relevant data is on the exchange server. In this case, you simply delete the user’s profile and recreate it. The email will be re-downloaded. If you’re worried about losing something back up the files first. – Appleoddity Mar 07 '19 at 13:07
  • Piling on here, the OST file is an exact offline copy of what is in the mailbox. There's no danger in deleting it. My guess is that the user moved the OST file but did not remove it from the Outlook profile, so Outlook is looking for it in the original location. – joeqwerty Mar 07 '19 at 13:48
  • Interesting, I was under the impression that the user somehow created a "local mailbox" and moved a lot of important mails there. What about "on this computer only" folders? Would there neccessarily be a .pst file etc. in that case? – jdm Mar 07 '19 at 16:00

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To avoid losing data, you can backup your mailbox to a PST file. Based on your situation, you can create a new profile. After configuring your account on new client and then import it.

Reference: Export or backup email, contacts, and calendar to an Outlook .pst file

Import email, contacts, and calendar from an Outlook .pst file

Perry
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