CentOS Errata and Security Advisory 2007:0775
https://rhn.redhat.com/errata/RHSA-2007-0775.html
The following updated files have been uploaded and are currently syncing to the mirrors:
s390: updates/s390/RPMS/mailman-2.1.5.1-34.rhel4.6.s390.rpm
s390x: updates/s390x/RPMS/mailman-2.1.5.1-34.rhel4.6.s390x.rpm