There are several possible causes for this code. 1)There is no route for the specified address space. For example, an SMTP ...

{4}: There are several possible causes for this code. 1)There is no route for the specified address space. For example, an SMTP connector is configured, but this address does not match. 2)DNS returned an authoritative host that was not found for the domain. 3)The routing group does not have a connector defined. Mail from one server in one routing group does not have a route to another routing group. 4)An SMTP protocol error occurred.