Mail Routing Issues with internal mail domains (4293585)

We have two Lotus Domino environment, one is for ABC and another for ZXY, we have built two coexistence accordingly and mail routing happening fine between Exchange –ZXY and Exchange –ABC and vice versa. The ask is ZXY users wants their primary SMTP address should be MAIL.ZXY.IE instead of ABC.IE after migrated on Exchange, but we are unable to do this because of incorrect mail address stamp.

Exchange(xzy.abc@ MAIL.ZXY.IE) gets converted to  ABC Notes (xzy.abc@ABC.IE) 

A migrated ZXY user sent mail to ABC Notes users, recipient able to receive email but with wrong address like @ABC.ie instead of @mail.ZXY.ie and end up with NDR when user reply to the sender, things are fine If I change back to @ABC.ie address as an primary address