[exim] Using more Routes in RoundRobin to send E-Mails

Hi, List!

This is my problem: I have 4 "outgoing-Server" by my provider, and I'd like to
send E-Mails from my Mail-Server using this Servers in a RoundRobin
configuration.

Unfortunately, I can't define a Cluster for these Servers, then there will be
administered by the provider and I can't configure anything.

Of course, I can define 4 routes with SmartHost for every Server, but how can I
say Exim to use them in RoundRobin (and, if a Server is dead, to ignore it)?

Is it possibile?

Thanks a lot!
Luca Bertoncello
(lucabert@???)