LinuxQuestions.org - sendmail behind router fails with 553 DNSBL

I am running Debian Sarge with sendmail V8.13.5. The Linux box is on a LAN behind a Belkin router connected to my ISP with DSL. I am able to send and receive mail on the local net but when I try to send a test message to my e-mail
address on my ISP it is being returned with a 553 message as follows:

The original message was received at Thu, 17 Nov 2005 19:05:49 -0500
from smmsp@localhost [127.0.0.1]

----- The following addresses had permanent fatal errors -----
<real email addy@ISP.net>
(reason: 553 5.3.0 ylpvm07,DNSBL:To request removal of, xx.xxx.xxx.xxx, send
the complete error message in an E-mail to removeme@ISP net)

where 'xx.xxx.xxx.xxx' is the dynamic IP address of the DSL connection. I have a feeling the error is caused because the ISP is unable to do a reverse DNS ron
my IP address and thus blocks the email thinking it is spam (DNSBL = Delivery Notification Spam Blocking List?). I do not have an MX record for my Linux box in any DNS server as 1) the box is behind the router and using DHCP and 2) the router itself gets a dynamic address from the ISP. I have opened up port 25 on the router but the results are the same.

Here is my sendmail.cm file:

divert(-1)dnl
#-----------------------------------------------------------------------------
# $Sendmail: debproto.mc,v 8.13.4 2005-06-03 16:49:22 cowboy Exp $
#
# Copyright (c) 1998-2005 Richard Nelson. All Rights Reserved.
#
# cf/debian/sendmail.mc. Generated from sendmail.mc.in by configure.
#
# sendmail.mc prototype config file for building Sendmail 8.13.4
#
# Note: the .in file supports 8.7.6 - 9.0.0, but the generated
# file is customized to the version noted above.
#
# This file is used to configure Sendmail for use with Debian systems.
#
# If you modify this file, you will have to regenerate /etc/mail/sendmail.cf
# by running this file through the m4 preprocessor via one of the following:
# * `sendmailconfig`
# * `make`
# * `m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf`
# The first two options are preferred as they will also update other files
# that depend upon the contents of this file.
#
# The best documentation for this .mc file is:
# /usr/share/doc/sendmail-doc/cf.README.gz
#
#-----------------------------------------------------------------------------
divert(0)dnl
#
# Copyright (c) 1998-2005 Richard Nelson. All Rights Reserved.
#
# This file is used to configure Sendmail for use with Debian systems.
#
define(`_USE_ETC_MAIL_')dnl
include(`/usr/share/sendmail/cf/m4/cf.m4')dnl
VERSIONID(`$Id: sendmail.mc, v 8.13.4-3 2005-06-03 16:49:22 cowboy Exp $')
OSTYPE(`debian')dnl
DOMAIN(`debian-mta')dnl
dnl # Items controlled by /etc/mail/sendmail.conf - DO NOT TOUCH HERE
undefine(`confHOST_STATUS_DIRECTORY')dnl #DAEMON_HOSTSTATS=
dnl # Items controlled by /etc/mail/sendmail.conf - DO NOT TOUCH HERE
dnl #
dnl # General defines
dnl #
dnl # SAFE_FILE_ENV: [undefined] If set, sendmail will do a chroot()
dnl # into this directory before writing files.
dnl # If *all* your user accounts are under /home then use that
dnl # instead - it will prevent any writes outside of /home !
dnl # define(`confSAFE_FILE_ENV', `')dnl
dnl #
dnl # Daemon options - restrict to servicing LOCALHOST ONLY !!!
dnl # Remove `, Addr=' clauses to receive from any interface
dnl # If you want to support IPv6, switch the commented/uncommentd lines
dnl FEATURE(`no_default_msa')dnl
dnl DAEMON_OPTIONS(`Family=inet6, Name=MTA-v6, Port=smtp, Addr=::1')dnl
dnl DAEMON_OPTIONS(`Family=inet, Name=MTA-v4, Port=smtp, Addr=127.0.0.1')dnl
dnl DAEMON_OPTIONS(`Family=inet6, Name=MSP-v6, Port=submission, Addr=::1')dnl
dnl DAEMON_OPTIONS(`Family=inet, Name=MSP-v4, Port=submission, Addr=127.0.0.1')
dnl
dnl #
dnl # Be somewhat anal in what we allow
define(`confPRIVACY_FLAGS',dnl
`needmailhelo,needexpnhelo,needvrfyhelo,restrictqrun,restrictexpand,nobodyreturn
,authwarnings')dnl
dnl #
dnl # Define connection throttling and window length
define(`confCONNECTION_RATE_THROTTLE', `15')dnl
define(`confCONNECTION_RATE_WINDOW_SIZE',`10m')dnl
dnl #
dnl # Features
dnl #
dnl # The access db is the basis for most of sendmail's checking
FEATURE(`access_db', , `skip')dnl
dnl #
dnl # The greet_pause feature stops some automail bots - but check the
dnl # provided access db for details on excluding localhosts...
FEATURE(`greet_pause', `1000')dnl 1 seconds
dnl #
dnl # Delay_checks allows sender<->recipient checking
FEATURE(`delay_checks', `friend', `n')dnl
dnl #
dnl # If we get too many bad recipients, slow things down...
define(`confBAD_RCPT_THROTTLE',`3')dnl
dnl #
dnl # Stop connections that overflow our concurrent and time connection rates
FEATURE(`conncontrol', `nodelay', `terminate')dnl
FEATURE(`ratecontrol', `nodelay', `terminate')dnl
dnl #
dnl # If you're on a dialup link, you should enable this - so sendmail
dnl # will not bring up the link (it will queue mail for later)
dnl define(`confCON_EXPENSIVE',`True')dnl
dnl #

dnl # Masquerading options
FEATURE(`always_add_domain')dnl
MASQUERADE_AS(`EMACH433.brazziel.net')dnl
FEATURE(`allmasquerade')dnl
FEATURE(`masquerade_envelope')dnl
EXPOSED_USER(`root')

dnl # Default Mailer setup
MAILER(`local')dnl
MAILER(`smtp')dnl
Cw emach433.brazziel.net
Cw brazziel.net

I've been working on this a couple weeks now, read the sendmail config stuff from sendmail.org and other docs with some measure of understanding. Please do not suggest using 'qmail', 'postfix' or some other package, those are not an option. Sendmail should work and that is what I'm trying to do. Any help with that is greatly appreciated. Thanks.