Hi @Amir Ben Shimol
I think if you use the Graph api in your application, you need to grant the required permissions to Onedirve or outlook's API.
For example, if you need to list all messages, then you need these corresponding API permissions
But the most fundamental problem is that your corporate user account still has insufficient permissions. You need to contact your administrator and ask him to grant you the corresponding permissions.
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Best Regards
Cheng Feng