[Exim] hostlist and dynamic IPs

I have a host that uses DynDNS . I want to allow it to relay
through my host ( many MXes dont accept mail from dynamic hosts
so they send through me).

I add 'host.dyndns.org' to a hostlist I will accept mail from, but
Exim seems to reverse lookup the hostlist to decide if a sender is
valid - which doesnt help in this case...

Is there a way to specify a hostlist to be *forward* looked up

i.e. if a host a.net is listed, which resolves to 1.2.3.4, then
accept mail from 1.2.3.4

?

( rather than :
reverse lookup 1.2.3.4 to '1234-modem_rack_a3.myisp.com'
find that '1234-modem_rack_a3.myisp.com' is not in the hostlist
refuse to relay
)

--
Pro is to con as progress is to Congress.
Rasputin :: Jack of All Trades - Master of Nuns