I am trying to retrieve the UPN for specific shared mailboxes on my O365 Tenant.  When I run the command:

Get-MailboxPermission -identity MyMailbox1

I get the following results...

Identity    User     AccessRights                                                                                     IsInherited Deny 
--------      ----       ------------                                                                                         ----------- ---- 
MyMailbox1    NT AUTHORITY\SELF    {FullAccess, ReadPermission}                   False       False

MyMailbox1    NT AUTHORITY\SELF    {FullAccess, ExternalAccount, ReadPermission}   False       False

MyMailbox1    Test User    {FullAccess}   False       False

.............etc

There are several users with the name "Test User" in the tenant.  I am looking to gather the actual UserPrincipalName or unique identifier that I can use.

Any suggestions?

Hi,

Please run the following command to get the detailed resulys about mailbox full access permission:

Get-MailboxPermission -Identity MyMailbox1 | fl

If it still doesn't return the information about "Test User", please check the user properties in ADUC (Active Directory Users and Computers). In Security tab, check the user list who has permission for this mailbox.

Regards,

Regards,