[Exim] Reading route_list from a plain text file?

Hi,

Is there any way I can read in from a file the domains to use in a
route_list? I've seen a rather long way of doing it using a dbm but
can anyone point me in the right direction??

I would have thought something like this:
route_list = partial-lsearch;/etc/exim/mail/domains.allmail

would work but obviously I'm missing something!!

Many thanks.

Jon Richardson