[Exim] secondary smarthost?

Hi,

I use a smart relay host for sending remote mails.
It's config:
----
smarthost:
driver = domainlist
transport = remote_smtp
route_list = "* smarthost bydns_a"

end
------
Can I use somehow a secondary smarthost if the 'primary' fails??

For example:

---
smarthost:
  driver = domainlist
  transport = remote_smtp
  route_list = "* smarthost1:smarthost2 bydns_a"
---
     Does it work ?

Or, should I set it in this way:
--------
smarthost1:
driver = domainlist
transport = remote_smtp
route_list = "* smarthost1 bydns_a"

smarthost2:
driver = domainlist
transport = remote_smtp
route_list = "* smarthost2 bydns_a"

end
------

Zoli