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Welcome to Microsoft Q&A.
Yes, it is possible to grant folder-level permissions in Outlook/Exchange, without giving you access to the entire mailbox.
Since you already have the access to already you supervisor needs to grant you folder level rights.
Here's how:
- Your Supervisor opens Outlook desktop client.
- Right-click the folder they want to share → Properties → Permissions.
- Add your name and choose your role (e.g., Editor = read/create/change items).
- If the folder is a subfolder, they may also need to give you “Folder Visible” on the mailbox root and Inbox, so you can navigate to it.