Can't Remove BESAdmin

I am trying to remove the BESadmin account from my network.  The BES Server was removed 4 years ago but nobody bother to remove the user.  Here is what I have done:

I removed BESAdmin from all Administrative groups
Then in the Exchange Power Shell I ran the following commands:

Remove-ManagementRoleAssignment -Identity "BES Admin EWS"
get-mailbox -ResultSize Unlimited | where {$_.ThrottlingPolicy -eq "BESPolicy"} | Set-Mailbox -ThrottlingPolicy DefaultThrottlingPolicy_a852ec1b-2fcf-4502-b690-c309c1a547cd
Get-ThrottlingPolicy BESPolicy | Remove-ThrottlingPolicy
Remove-ADPermission -InheritedObjectType User -InheritanceType Descendents -ExtendedRights Send-As -User "BESAdmin" -Identity "DC=domain,DC=local" (replacing domain and local appropriately)
Remove-RoleGroupMember "View-Only Organization Management" -Member "BESAdmin"
Get-MailboxDatabase | Remove-ADPermission -User "BESAdmin" -AccessRights ExtendedRight -ExtendedRights Receive-As, ms-Exch-Store-Admin

Now I am trying to run:

Get-Mailbox -ResultSize Unlimited | Remove-MailboxPermission -AccessRights FullAccess, sendas -User "domain\besadmin"

But it keeps failing with "Warning:  Can't remove the access control entry on the object for account "domain\besadmin" because the ACE doesn't exit on the object"

If I try to remove the Send As permission using the console, I get the following error:

Active Directory operation failed.  This error is not retriable.  Additional Information:  Access is denied.

So what rights have I failed to removed?  Thank you!