Office 365 - Mail and Calendar folder permission levels
If someone has shared a mail folder or their calendar with you or designated you as a delegate for that folder/calendar, then you have permission to perform certain activities in that folder/calendar. The extent of the activities you can perform mail folder or calendar you are a delegate for, depends on your role (or combination of permissions) for that mail folder/calendar.
Mail folder permission levels
Owner: Create, read, modify, and delete all items and files, and create sub-folders. As the folder owner, you can change the permission levels others have for the folder. (Does not apply to delegates.)
None: You have no permission. You cant open the folder.
Contributor: Create items and files only. The contents of the folder do not appear. (Does not apply to delegates.)
Reviewer: Read items and files only.
Non-Editing Author: Full read details. Create items. Delete own items. Folder visible.
Publishing Editor: Create, read, modify, and delete all items and files, and create sub-folders. (Does not apply to delegates.)
Editor: Create, read, modify, and delete all items and files.
Publishing Author: Create and read items and files, create sub-folders, and modify and delete items and files you create. (Does not apply to delegates.)
Author: Create and read items and files, and modify and delete items and files you create.
Custom: Perform activities defined by the folder owner. (Does not apply to delegates.)
Note - With author or editor permissions, a delegate has send-on-behalf-of permission. Sent messages contain both the managers and delegates names. Message recipients see the managers name in the Sent On Behalf Of box and the delegates name in the From box.
Calendar permission levels
Note: The list below contains names of permissions levels in Outlook on the web - Outlook desktop client, respectively.
Availability only - Free/Busy time: Allows someone to view blocks of time as Free, Busy, Tentative, Away.
Limited Details - Free/Busy time, subject, location: Allows someone to view your Subject and Location. Events set to private will only display as Private Appointment to viewers.p>
Full Details - Reviewer: Allows someone to view your Subject, Location, Attendees, and Description. However, any event you mark as private displays simply as Private Appointment to viewers.
Editor - Editor: Provides read/write/modify access.
Delegate - Owner: In addition to "Editor" permissions, a delegate can also be selected to receive calendar notifications/requests/invitations. By default, 'Delegates' cannot view/modify events set to Private. You do have the option to grant the delegate the ability to view (full details) Private events.