OUTLOOK OST PATH change

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According to your description, I have tested on my outlook 365 client by registry and successfully modified the path of the .ost data file. Please refer to the following steps to check whether it is different from your operation:
1.Select Start, select Run, type regedit in the Open box, and then select OK;
2.Locate and then select the registry subkey: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook;
3.Right-click Outlook, select New, and then select Expandable String Value;
4.Type ForcePSTPath, and then press Enter;
5.Right-click ForcePSTPath, and then select Modify.
6.In the Value data box, type the full path of where you want to store the .ost file (such as D:\MyOST), and then select OK;
7.Exit Registry Editor;
8.Control Panel>Mail>Show Profiles…>Add…>type a name for the new profile>choose Manual setup or additional server types and configure your IMAP account;
9.Back to Mail window, choose Prompt for a profile to be used;
10.Open outlook and choose the new profile.
(It should be noted that if you modify the registry by mistake, serious problems may occur. Please back up the registry before operation.)