[Exim] accept hosts = ... : /path/to/file : ...

I use
accept hosts = +relay_hosts
where
relay_hosts = ... : /path/to/relay/hosts/file : ...

The problem is that sometimes a hostname gets into the file that doesn't
have an A record and then everything after the "bad" hostname gets
ignored. Would using an lsearch lookup cause Exim to do a reverse
lookup on the incoming IP address rather than a forward lookup on the
hostnames in the file? Does Exim automatically look for both the
hostname and the IP address?

As a workaround I'm not adding hostnames to the file if they don't have
A records. I'm thinking this is not a bad idea in any case.
Thanks,
John Dalbec