Once upon a time in Qatar, I was wondering if I can remove the internal IP addresses from the messages headers, as I saw it at that time as a security breach to expose the internal IP addresses to the external world maybe a way to help penetrators doing their job :)
I went through this article at Microsoft Technet, and it's recommended to read this article, fabulous!
To get the internal names and IPs in a message through outlook, right click the message in the left pane and choose properties, and you will find all internal data, and in OWA for Exchange 2007, It's included in the Exchange 2007 only OWA, a button called Message Details that will do the job fine on web access
the command will stripe the internal IPs and hostnames from the message sent from your internal network, what it does in the background is it remove the anonymous permission from the ms-Exch-Send-Headers-Routing attribute from the receive connector by this command:
Get-SendConnector "Connector Name" | Remove-ADPermission -AccessRight ExtendedRight -ExtendedRights "ms-Exch-Send-Headers-Routing" -user "NT AUTHORITY\Anonymous Logon