This question came from an administrator who needs to give a user Send As permissions but doesn't want the user have permission to the other user's Inbox.
We're using Office 365 and want to allow a user to send on behalf of someone else but don't want them to be able to access that person's Inbox. We tried Delegate permissions but what is the special combination of properties in the Inbox permissions that can be set to allow them to Send As that user but not able to open the other user's Inbox?
For this you won't use Delegate permissions. You need to give the user Send As permission on the other user's mailbox and you'll need to do this on the server, not in Outlook. Because you are using Office 365, you'll need to use the Add-RecipientPermission cmdlet since you don't have access to the Exchange Management Console. The format will be like this, where Bob Smith is the name of the mailbox that Sally Jones needs to Send As.
Add-RecipientPermission "Bob Smith" -AccessRights SendAs -Trustee "Sally Jones"