Not sure whether this will work, but do you have a third email account you could use? Use the third email account on the one account - to basically "clear" the email address that you want to use. Then, use the "cleared" email account on the DL account you want it to go to. I'm hoping this is not sounding like Abbott and Costello's Who's on First skit. :)

Hey you might want to publish in the troubleshoot section so more troubleshooters can see this. No answer to your question though. Sorry!