Cant open Exchange 2013 mailboxes by Exchange 2010 user, using MFCMAPI tool

Hi,
I want to create superadmin user, which is capable of accessing all mailboxes in AD.
With this account, I want to open information store of each mailbox(from MFCMAPI).

I am facing issue, while opening Exchange 2010 user's mbx , if superadmin hosts on Exchange 13 and vice-versa.

I tried

Get-MailboxDatabase  | Add-ADPermission -user Domain\User  -AccessRights GenericAll  -InheritanceType All

and

Get-MailboxDatabase -includepreExchange2013  | Add-ADPermission -user Domain\User  -AccessRights GenericAll -InheritanceType All

*This is not for blackberry

ManojK