I have an issue with a case similiar to problem mentioned in here:
Microsoft Graph “Access is denied. Check credentials and try again” in C#
As mentioned in the case I’ve changed the permission from Delegated to Application as my team is trying to create exterial app sending message from Exchange Online mailbox. When changing to application permission everything works except the app has too wide permission – it can sent message as anybody in the company. It is a solution but I’m concerned about security issues.
As I try to configure it as Delegated permission there is still error with access denied.
Can you tell me how to configure app permission to cut the permission as it should be – only for one mailbox for sending, reading and moving messages in mailbox?