Creating a Custom HubTransport Connector on Exchange 2013 Multirole Server Results in:
421 4.3.2 Service not available
Connection to host lost
In this video we demonstrate one of the common problems that you might hit when creating new (or re-creating existing Exchange 2007) Custom Receive Connectors in Exchange 2013 Multirole Servers. In our example, we are creating a Custom Relay connector which allows relaying for a specific internal host/application. The problem occurs when you choose the “HubTransport role” for the connector type. In this case, the Default Frontend connector, which is the common messaging entry point for the organization, closes connections from remote email servers with “421 4.3.2 Service not available” and effectively rejects accepting inbound e-mails. As you can see, the solution is to delete the Custom HubTransport Receive connector and re-create it again as a FrontendTransport connector.