private boolean isHostUnknown(String recipient) {
        boolean host_unknown = !domainPair.getLocal().equals(recipient);
        // If the recipient does not match the local domain then check if it matches a subdomain. This
        // trick is useful when subdomains of this server are registered in the DNS so remote
        // servers may establish connections directly to a subdomain of this server
        if (host_unknown && recipient.contains(domainPair.getLocal())) {
            host_unknown = !routingTable.hasComponentRoute(new JID(recipient));
        }

        if (host_unknown) {
            host_unknown = !Trunking.isTrunkingEnabledFor(recipient);
        }
        return host_unknown;
    }
Returns true if the domain requested by the remote server was validated by the Authoritative
Server. To validate the domain a new TCP connection will be established to the
Authoritative Server. The Authoritative Server may be the same Originating Server or
some other machine in the Originating Server's network.<p>

If the domain was not valid or some error occurred while validating the domain then the
underlying TCP connection may be closed.

@param doc the request for validating the new domain.
@param streamID the stream id generated by this server for the Originating Server.
@throws StreamErrorException when validation did not succeed.
xmppserver/src/main/java/org/jivesoftware/openfire/server/ServerDialback.java