The following errata for CentOS-2 have been built and uploaded to the centos mirror:

RHSA-2006:0265-01 Critical: sendmail security update

Files available:
sendmail-8.12.11-4.21AS.8.i386.rpm
sendmail-cf-8.12.11-4.21AS.8.i386.rpm
sendmail-devel-8.12.11-4.21AS.8.i386.rpm
sendmail-doc-8.12.11-4.21AS.8.i386.rpm

More details are available from the RedHat web site at
https://rhn.redhat.com/errata/rh21as-errata.html

The easy way to make sure you are up to date with all the latest patches is to run:
# yum update