[Exim] Deny Hosts List

I need help setting up an acl to deny known bad hosts.

Under acl_check_data: I have:

  deny message = sender IP address $sender_host_address is locally blacklisted \
                 here. If you think this is wrong, get in touch with postmaster
          !acl = acl_whitelist_local_deny
           hosts = ${if exists{CONFDIR/local_host_blacklist}\
                              {CONFDIR/local_host_blacklist}\
                              {}}
          log_message   = "BLACKLIST: $sender_fullhost"

And local_host_blacklist contains entries like:

    217.205.170.210
    61.241.148.11
    *.attbi.com
    *.cable.mindspring.com
    mail.ru

I have two questions:

1. Do I need an lsearch on the local_host_blacklist file if I dont use
        <> : <> : ...
    syntax? Lsearch seems to be for key/value pairs though. I'm stuck.
2. Is it wise to block hosts such as *.cable.mindspring.com? We are a
   UK-based business, and it is very unlikely that we will receive mail
   from a cable user in this domain.

Advice gratefuly received.
Rory

--
Rory Campbell-Lange
<rory@???>
<www.campbell-lange.net>