If you are using the new version of mailman, you have to start mailmanctl (it took me a while to find it, too). For a one-time-start it's enough to call bin/mailmanctl start in the mailman home directory.

To have it started on each reboot you must include it in the /etc/init.d directory (or whatever it is called in RedHat). The INSTALL file in the directory where you unpacked your mailman describes this very well.

-- Jean Bausch