The mailman package is configured on sedna, to configure/modify mail lists, logon to sedna as root:

ssh -oGSSAPIAuthentication=yes root@sedna.astro.columbia.edu

Creating a Mail List

[0 root@sedna root]# newlist
Enter the name of the list: mail list name
Enter the email of the person running the list: user@astro.columbia.edu
Initial astrobiology password:  (prepare a password using the 'pwgen 8 1' command on any CW)
Hit enter to notify mail list owner...
[0 root@sedna root]# /usr/local/sbin/mailmanrepair
[0 root@sedna root]# 

Note the invocation of /usr/local/sbin/mailmanrepair: 
this sets up the proper aliases so that postfix knows to let mailman handle the relevant addresses.

Removing a mail list

Run the 'rmlist' script to remove a mailing list. By default, a list's archives are not removed unless the --archives option is given. Remove the components of a mailing list with impunity - beware! This removes (almost) all traces of a mailing list. By default, the lists archives are not removed, which is very handy for retiring old lists.

[1 root@sedna sbin]# rmlist 'name of mail list'
Not removing archives.  Reinvoke with -a to remove them.
Removing list info
[0 root@sedna root]# /usr/local/sbin/mailmanrepair
[0 root@sedna sbin]#

Note the invocation of /usr/local/sbin/mailmanrepair. This is used to tell postfix that the new addresses that should be handled by postfix.