[Exim] Allowing relay by sender ip

Hi,

In setting up exim in conjunction with ipass, i need to enable relaying
based on the ip addresses contained within a dbm file. I noticed that in
some previous postings, sender_net_accept_relay is mentioned, but this
doesn't seem to be a valid option ?
I'm probably being daft, but could someone point me in the right direction...

Cheers,

Tristan.