[exim] route_list and hosts_randomize

Hello,

to share the load on our smarthosts, we could either use a route_list
with several smarthosts and hosts_randomize=true an the clients, or we
could use route_list with e.g. smarthost.com which resolves to several
ip-addresses so we don't have to change the exim-configuration just to
add or remove a certain smarthost. But I'm not sure about the benefits
or drawbacks of both ways. Would the second way work fine, or would exim
cache dns-lookups too long, so that changes of available smarthosts
wouldn't come in effect in time?

Regards
Marten