Sorry for more techno mumbo jumbo but everytime I end up spending more than an hour looking for a simple answer I feel obligated to put the answer online. So here was my problem.
In Exchange 2007 I set up a Quarantine Mailbox for all the anti-spam messages coming in on our Transport Server. The problem though was when sorting through the quarantine, I would hit “Send Again” to release the message from the quarantine, but doing so would put the actual email address of the Quarantine Mailbox rather than the original sender address in the message. This was super annoying since this meant that people were responding to a spam mailbox, rather than the original sender.
The solution was a super easy one. Even though I had set up the Quarantine mailbox on the Transport Server I hadn’t touched the Hub Transport server. So All I had to do was run the following line in the command shell on one of the hub transport servers in the domain:
Set-ContentFilterConfig -QuarantineMailbox <SMTP Address>
With that done the Hub Transport Server was able to identify the quarantine mailbox as something other than a standard mailbox and then SendAs began functioning as expected.
Viola! Hopefully that saved you a little effort if you happen to have had that narrow and exact similar problem.