I think I understand what the OP is claiming. But its not a problem with the system, rather wrong expectations of the OP.
He set up his
account. He configured multiple other accounts to forward to that address. FORWARD being the key word. The other accounts are sending an email to his
account. If he replys to one of those messages it works in the opposite manner. The
account sends the response to the other account and they send it to the desired reply address.
If you look at the header of the email you will see the
account because the messages were FORWARDED to it. I think this is what he is complaining about.
Basically the OP needs to stop forwarding emails to the
account account and setup those accounts on the BIS site. Those messages will then come and go from the device without the extra forwarding steps that would show the forwarding trail within the header of the message.