The following errata for CentOS-2 have been built and uploaded to the centos mirror:
RHSA-2006:0515-01 Important: sendmail security update
Files available: sendmail-8.12.11-4.21AS.10.i386.rpm sendmail-cf-8.12.11-4.21AS.10.i386.rpm sendmail-devel-8.12.11-4.21AS.10.i386.rpm sendmail-doc-8.12.11-4.21AS.10.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