How to Reset Mailbox Permissions?
The Reset Mailbox Permissions feature allows you to reset all non-owner mailbox permissions (Full Access, Send As and Send On Behalf) for the selected set of Mailboxes.
Perform the following steps to Reset Mailbox Permissions:
Select Office 365 Manager from the available vertical tabs. Then from left side of the application, select Mailbox Permissions and then click on Reset Mailbox Permissions.
On selecting "Reset Mailbox Permissions", a pop - up window is displayed as shown below:
 

     
  • Select the Mailboxes for which you want to reset all non-owner mailbox permissions and Click on the OK button to proceed.