[exim] reverse dns lookup not functioning?

Dear all,

I found some emails without right reverse dns lookup still come
through into my email box even though I set up exim to do reverse dns
lookup. Here is an example in the exim log:

2005-04-13 10:45:37 no host name found for IP address 61.141.241.162
2005-04-13 10:46:13 1DLlwH-0003Ae-TI <= asdfg122357@???
H=(sina.com) [61.141.241.162] P=esmtp S=806
2005-04-13 10:46:22 1DLlwL-00040G-Fk <= asdfg122357@??? U=hongyu
P=local-bsmtp S=1199
2005-04-13 10:46:22 1DLlwL-00040G-Fk => <forward@???>
R=virtual_user T=virtual_userdelivery

This IP address 61.141.241.162, which appeared in the first line of
the log being errored for no host name, still went on again in the
second line sending the email to my address forward@???

Here is the line of reverse lookup in /etc/exim.conf

host_lookup = 0.0.0.0/0

Is the reverse dns lookup functioning or not?

Appreciate your help!