[exim] greylisted due fallback server

In sending to a list i noticed my messages were greylisted and delayed a
lot of time.
It turned that they used a system that refuse with a 4xx error any message
the first time that arrives from an "unknown" server and after 5 minutes
it begin to accept mail fron that server.
It did not worked for me since in my setup I have:

begin routers

lookuphost:
driver = dnslookup
domains = ! +local_domains
pass_on_timeout
self = fail
fallback_hosts = vettore.xxx.it
transport = remote_smtp
no_more

smart_route:
driver = manualroute
domains = ! +local_domains
route_list = * vettore.xxx.it bydns
transport = remote_smtp
no_more

--

this way if for some reason the connection cannot be get on the first time
the messages are passed to the server vettore, that is on a different
network so it has different chanches to connect.
Unfortunately this is setup so vettore know that if a message arrive to it
it has passed a first try, so when it tries again it know is the second
try and so the delay between the second and the third try is one hour.
It happens that some messages bounced with 4xx are then passed to the
secondary server, so the messages are tried first time by main server,
after 5 minutes by secondary server, and then each hour, thre hours, etc.
In this case is possible that the greylisting count is reset so the
message never passes !

I contacted the administrator of the remote server and they replied that
my server does not respect RFC since after a 4xx does not retries but just
pass the burden to a different server, that in turd has a larger timeout.
This is not clear to me. Is it true ? I knew that timeouts are minumum,
not maximum, and that i never found a RFC saying that if a remote server
says 4xx you con retry only with the same source address.
Any answer ? If i am wrong, how to change the config file ?