Hi @S S ,
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According to your description, I have searched the relevant registry and I didn't find any settings to change the location of the NST file by registry or group policy. And I have done a lot of research and test, unfortunately I didn't find any useful suggestion to relocate the NST file.
As I know, the NST file is created when you access a Group in Outlook the first time, and stores your Groups conversations and other local Groups data. It is not recommended that you change the path of this file to avoid unexpected trouble.
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