I have been handballed an issue post an Exchange 2003 to Exchange 2010 migration. The old exchange server has been completely decommissioned as far as I can tell.
The remaining issue is that now any user can send as any other user despite the permissions not being in place.
I have checked the ADSIEdit.msc permissions as detailed here:
http://social.technet.microsoft.com/Forums/exchange/en-US/df365e57-80b0-4d60-890d-72c36742b072/mailbox-permissions-send-as-anyone-can-send-as-anyone?forum=exchange2010
I have checked all other user permissions that I can find.
There seem to be a lot of articles with people having a similar issue but none with a common resolution.
Is anyone able to help with this?