Migrating from LotusNotes to exchange 2010. Have both servers running and sharing SMTP namespace. Mail works fine but there is an issue with NDR messages looping between the two mail servers.
Each server is not authoritative and relays emails with unkown addresses at our domain to each other.
In this way mail can flow between LotusNotes users and Exchange users both with the same domain name. The problem is with messages to addresses that don't exist on either server.
Since neither server is authoritative for the domain they won't NDR anything and thse emails just loop between the two servers.
How can I fix this?