If you are an Exchange administrator and are having trouble in accessing other mailboxes although you have full access, then you may find that you need to remove the “Deny” permission on the mailbox you are trying to access. Sometimes this can be your own account or maybe a group like “Domain Admins”.
To check the existing permissions on the mailbox, you can use the script below within the Exchange Management Shell (EMS):
Get-MailboxPermission -identity [Mailbox-Alias]
[Mailbox-Alias] = Alias of the mailbox you want to check the permissions on
One you have identified the permissions you want to change, you can now carry out the change using the script below within EMS:
Remove-MailboxPermission -identity [Mailbox-Alias] -user [User to remove] -AccessRights FullAccess -Deny
[Mailbox-Alias] = Alias of the mailbox you change to change the permissions on
[User to remove] = The user (or user group) you want to remove the Deny permissions for