Give one user full control of another user’s mailbox in Office 365

To give yourself or another user full access to someone else’s mailbox in Office 365 you have to use powershell. It can’t be done online.

Mailbox access

In this example we are going to give Pieter full access to the mailbox of Danielle use this command:

Add-MailboxPermission  -User -AccessRights FullAccess

Inbox access

As an alternative you can also give permissions to an inbox only

Here’s the code:

Add-MailboxFolderPermission -Identity\Inbox -User -AccessRights Owner


For more detailed information, please refer below article:

Give an Administrator the Ability to Open and View the Contents of a User’s Mailbox( )