In a recent emergency situation at one of our offices (power outage) mail was stacking up at our head office as it couldn't get through. So we changed the home mail server in the person documents for those who had replicas on the head office server, so that new mail would route there.
It didn't - mail just stacked up in mail.box awaiting the remote server connection to come alive again.
Restarting the router task had no effect.
AIUI when the router processes an incoming email it looks in the NAB to find which server to route it to. Is there a cache that needs flushing that survives a router restart? Or have we missed something?