I was trying the doc at
[SOLVED] Zimbra+Mailman Howto first but since it didn't work, I reluctantly tried ZCS Mailman Integration - Zimbra :: Wiki.
I say reluctantly because I hate the idea of running two machines for only a handful of lists.
Anyway, I believe there is a slight error in the Wiki page. I had to change the line that says:
zmprov ma LIST_NAME@EMAIL_DOMAIN zimbraMailTransport MAILMAN_HOSTNAME
to
zmprov ma LIST_NAME@EMAIL_DOMAIN zimbraMailTransport smtp:MAILMAN_HOSTNAME:25
otherwise the transport would fail.
Thanks,
Doug