I have a system that has been upgraded from Red Hat Linux 9 to Scientific Linux 6.2.
Red Hat Linux 9 -> Fedora Core 1 -> FC2 -> FC3 -> FC4 -> FC5 -> Centos 5 -> Scientific Linux 6.2
I must confess though that there are some old 'mailman' mailing lists on that thing that I am afraid to mess with. The way 'mailman' is configured changed somewhere along the way.