[EXIM] Fallback Hosts did not work

Hello all......
Below is the setup I have for one of our primary mail servers with its fallback
host. The hssmtp4 system did fail last night, and the hssmtp2 did not get any
mail sent to it.
Is there anything in this setup that I have missed?
Thanks again for all of the help.
Paul Yahnig

hub_route_NOTES:
driver = domainlist
transport = remote_smtp
route_list = hssmtp4 $domain byname
fallback_hosts = hssmtp2 $domain byname