[CentOS] CentOS-6, Postfix and Mailman

We have a bunch of lists hosted on a CentOS-4.9 server
running sendmail and mailman that we are moving to a
CentOS-6 vm running postfix and mailman.  I am testing the
setup and I am running into a problem no doubt caused by
my own ignorance wrt postfix.

Based on groking the web I discovered that the recommended
way to configure postfix to work with mailman is a script
called postfix-to-mailman.py. I installed and modified
this script to suit our installation.  I followed the
instructions therein and made the recommended changes to
posfix, to wit:

# postfix-to-mailman.py
MailmanHome = "/var/lib/mailman";        # Mailman home
data directory

# Add mailman virtual domains to transport
# /etc/postfix/transport:
#   mailman.ourdomain.tld   mailman:
#   mailman.other.tld       mailman:
#
# /etc/postfix/main.cf:
#    inet_interfaces = localhost, mailman.ourdomain.tld, ...
#    relay_domains = mailman.ourdomain.tld, ...
#    transport_maps = hash:/etc/postfix/transport
#    mailman_destination_recipient_limit = 1
#
# /etc/postfix/master.cf
#    mailman unix  -    n    n    -    -    pipe
#      flags=FR user=mailman:mailman
#      argv=/var/mailman/postfix-to-mailman.py ${nexthop}
${user}

The mailman web interface is setup and works.  The
mm_cfg.py file was altered to handle the virtual domains
of the mailing lists.  Adding a new list via the web
interface generates and successfully delivers via our mail
hub the new list instructions to the owner's email.
Similarly, adding a new user via the web interface
generates and successfully delivers a welcome email.

However, email to the test mailing list does not get
processed by mailman.   This is what I see in
/var/log/maillog:

/var/log/maillog:Mar 22 14:53:53 inet08
postfix/smtpd[2785]: E248860A9A:
client=inet06.hamilton.harte-lyne.ca[216.185.71.26]
/var/log/maillog:Mar 22 14:53:53 inet08
postfix/cleanup[2789]: E248860A9A:
message-id=<201203221853.q2MIrrV5026005 at inet06.hamilton.harte-lyne.ca>
/var/log/maillog:Mar 22 14:53:54 inet08
postfix/qmgr[2519]: E248860A9A:
from=<root at inet06.hamilton.harte-lyne.ca>, size=563,
nrcpt=1 (queue active)
/var/log/maillog:Mar 22 14:53:55 inet08
postfix/error[2792]: E248860A9A:
to=<test at mailman.byrnejb.ca>, relay=none, delay=1.3,
delays=0.11/1.1/0/0.07, dsn=4.3.0, status=deferred
(unknown mail transport error)

The script postfix-to-mailman.py says that entries in the
aliases map are not required for it to work.  So, I did
not create any.

As I am completely unfamiliar with postfix I cannot
interpret the errors I am seeing.  It appears that mail is
routed correctly to the posfix server but that the
delivery agent, presumably mailman, is not working or
postfix is unable to connect to it.

Does anyone here have experience getting postfix and
mailman working together and, if so, how does one do it? 
Is postfix-to-mailman.py the proper way to do this or not?
 Should there be entries in the postfix aliases map for
mailman?

-- 
***          E-Mail is NOT a SECURE channel          ***
James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
Harte & Lyne Limited          http://www.harte-lyne.ca
9 Brockley Drive              vox: +1 905 561 1241
Hamilton, Ontario             fax: +1 905 561 0757
Canada  L8E 3C3