[Exim] default behavior of failed delivery to a smart host

Hi,

Working with the domainlist router and smarthosts, I've noticed there is an
option for failed deliveries called "host_find_failed" that can be set up
in a configuration thusly:

smarthost:
driver = domainlist
transport = remote_smtp
route_list = * 111.111.111.111 byname
host_find_failed = freeze

There are 3 other switches that can be used besides "freeze" including:
defer, pass, and fail.

I was wondering what the default behavior of the router would be if the
"host_find_failed" option were not used here, and the smarthost were
unreachable for any reason. I've lost mail using the smarthost option in
Sendmail, so I'm curious about this functionality.

Does anyone know this?

Thanks.

Regards,
Steve Romero