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( )

Open another user’s mailbox in Office 365

In Office 365 you can open anoth­er user’s mail­box. Here’s how.

Go to the out­look web access page. In the left col­umn find your user­name and right click on it.

Right click on your user­name













Then select “Oth­er user’s inbox”

Select other user's inbox
Select oth­er user’s inbox












In the dia­log box that appears, enter the name of the desired mail­box or use the address­book icon to do a full search.

Enter the name of the desired mailbox
Enter the name of the desired mail­box






And click OK. Now you will see the oth­er user’s mail­box appear in the left col­umn.

There's your other user's mailbox
There’s your oth­er user’s mail­box














When you receive an error stat­ing that you have no per­mis­sion to open the inbox when you are sure it exists, you may need to get the right per­mis­sions from your admin­is­tra­tor.

Not found or no permission
Not found or no per­mis­sion






I also have an arti­cle that explains how to set the right per­mis­sions.

Read it here.