Exim RBL check / lsearch oddity

I have been using this stanza in exim.conf for checking against RBLs but to exclude authenticated users:

Code:

  deny   message = rejected because $sender_host_address is in a blacklist at $dnslist_domain see $dnslist_text
         !hosts = +relay_hosts
         !authenticated = *
         dnslists = bl.spamcop.net : sbl-xbl.spamhaus.org : relays.ordb.org : list.dsbl.org

I discovered today that IP addresses appearing in /etc/relayhosts were still being checked in the dnslists even though the line !hosts = +relay_hosts suggests they shouldn't. (relay_hosts is defined as: hostlist relay_hosts = lsearch:/etc/relayhosts : localhost)

On investigation with exim -bh <blacklisted.IP.in.relayhosts>, I found that a hostname check, not an IP check was being done against /etc/relayhosts. After a bit of trial and error, I discovered that the lsearch was causing this to happen because using:

Code:

hostlist rbl_whitelist = /etc/relayhosts : localhost

would work as expected.

Any comments as to why lsearch would cause such dramatically different behaviour?

Here are some snippets from exim -bh showing the debug output. 1st using lsearch:

Code:

>>> processing "deny"
>>> check !hosts = +relay_hosts
>>> sender host name required, to match against lsearch;/etc/relayhosts
>>> looking up host name for 212.60.x.x
>>> IP address lookup using gethostbyaddr()
>>> IP address lookup failed: h_errno=1
LOG: no host name found for IP address 212.60.x.x
>>> host in "lsearch;/etc/relayhosts : localhost"? no (failed to find host name for 212.60.65.174)
>>> host in "+relay_hosts"? no (end of list)
>>> check !authenticated = *
>>> check dnslists = bl.spamcop.net : sbl-xbl.spamhaus.org : relays.ordb.org : list.dsbl.org

Now without lsearch:

Code:

>>> processing "deny"
>>> check !hosts = +rbl_whitelist
>>> gethostbyname looked up these IP addresses:
>>>   name=localhost address=127.0.0.1
>>> host in "/etc/relayhosts : localhost"? yes (matched "212.60.x.x")
>>> host in "+rbl_whitelist"? yes (matched "+rbl_whitelist")
>>> deny: condition test failed