[Exim] relaying problem (with mailman)

(
# exim -bV
Exim version 3.32 #1 built 15-Aug-2001 00:13:26
Copyright (c) University of Cambridge 2001
)

I've scoured the web trying to find TFM I could R in order to solve this
problem, without any luck.

I have a machine hiding behind a router. I have a domain name
(lithchat.com) that points to that router. All smtp calls are bumped to
this machine (nida), with an IP address of 192.168.0.6

All mail to blah@??? behaves as expected.

However, when someone sends a message for mailman to process, I get this
error in smtp-failure (mailman log file):

Oct 28 00:09:24 2001 (2789) delivery to tester-owner@??? failed
with code 550: 5.7.1 <tester-owner@???>... Relaying denied. IP
name lookup failed [192.168.0.6]

And the message never gets delivered. The mailman queue runner just
keeps trying to deliver.

The message appears in the exim/mainlog as this (this is from a diff,
though similar, message):

2001-10-29 10:40:03 15yFSF-0004Ud-00 <= moacir@??? H=(zuikis.uchicago.edu) [128.135.57.157] P=esmtp S=495 id=200110291641.KAA20872@???
2001-10-29 10:40:04 15yFSF-0004Ud-00 => tester <tester@???> D=list_director T=list_transport 2001-10-29 10:40:04 15yFSF-0004Ud-00 Completed



Here are my seemingly appropriate exim.conf settings:

local_domains = 192.168.0.6:127.0.0.1:64.195.32.161:nida:lithchat.com

local_domains_include_host = true
local_domains_include_host_literals = true

relay_domains = 192.168.0.0/24:*.lithchat.com

relay_domains_include_local_mx = true

list_director:
driver = smartuser
require_files = MAILMAN_HOME/lists/${lc:$local_part}/config.pck
transport = list_transport

list_transport:
           driver = pipe
           command = MAILMAN_WRAP post ${lc:$local_part}
           current_directory = MAILMAN_HOME
           home_directory = MAILMAN_HOME
           user = MAILMAN_UID
           group = MAILMAN_GID

------------

And from /etc/hosts:

127.0.0.1       nida                    nida.lithchat.com       
192.168.0.6     nida.lithchat.com       nida

-----------

Any idea about what I might be doing wrong? What makes the mail not get
delivered, saying relaying denied? And, most importantly, why did this
work in the past? (as of three weeks ago)

TIA,

--m