Automatic download of pictures in OWA and Outlook 2010 not allowed with internal addresses via PowerShell

Hello,

We are on Exchange 2010 and Outlook 2010.

The problem is  that the internal address which is a mailbox account will not add. The Outlook 2010 GPO is not reliable, plus it doesn't capture OWA users. I need to allow pictures to automatically download from a internal safe sender account.

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Set-MailboxJunkEmailConfiguration -Identity user -TrustedSendersAndDomains @{Add="corporatecommunication@domain.com"}
Property validation failed. Property = TrustedSendersAndDomains (System.String)
Error = "corporatecommunication@domain.com" is in your organization and can't be added to Safe Senders and Recipients..+ CategoryInfo          : NotSpecified: (0:Int32) [Set-MailboxJunkEmailConfiguration], PropertyValidationException+ FullyQualifiedErrorId : 2696E7D7,Microsoft.Exchange.Management.StoreTasks.SetMailboxJunkEmailConfiguration

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Any ideas?