Where is limit specified on ReceiveConnector to allow maximum number on IPs to be allowed in Relay .. we've been getting following error on adding any new IP on relay in receive connectors... is there a way to increase this limit ? Few out have suggested us to create a new connectors and others apart say to go with sub-net CIDR (Classless Inter-Domain Routing) approach but I believe not a good way to go with CIDR as we have a list of approx 1200 IPs in this particular connector popping out the error at the moment. Please suggest. 

1200 allowed IPs is alot. I dont think you can increase that. I woudl do exactly what others have suggested. New Connectors or CIDR. With that many allowed, I dont think it matters which way you want to go, its a matter of management.