We`ve recently installed office 365 and taken the opportunity to change domain name from xxxp.co.uk to xxxa.co.uk. All users are the same so have changed to John.Smith@xxxa.co.uk. I`m having an issue with some users still sending emails to John.Smith@xxxp.co.uk. I`d like to either reject that via the OA365 Exchange or at a user level but struggling with concept. Any pointers gratefully received.