[exim] dnslists - how to set timeouts

Hello,

I'm using dnslists to check against RBLs and it works fine most of the
time. But sometimes the DNS lookups seem to take too long so for the
client it seems as if our SMTP-server is not responding and then it
timeouts the request. Is there a way to set a timeout and when the RBL
nameservers couldn't be contacted it will be treated as if there is no
entry in the RBL list?

Regards
Marten