CentOS: Red Hat Enterprise Linux, Minus Red Hat - page 4
Getting Something For NothingConsistency in an uncertain world has its own weird appeal, even when it's for the wrong things. CentOS runs a number of default services that it shouldn't, like mdmonitor for RAID monitoring and management on systems that don't even use RAID; sshd; bootpc; and xinetd when it is not managing any services. Run netstat --inet -a to see what your CentOS system is listening for; you'll get an eyeful. Sure, these might all be things you want to have running. If that's the case, it's generally wiser to have to turn them on. Old-fashioned security-minded admins go by "deny all, allow as needed."
Sendmail still lingers like a houseguest that won't leave, like a squatter that you can't evict. The only way to get rid of Sendmail is after installation, even with a completely custom installation. This is puzzling, since Postfix is also an installation option. To use Postfix, you must first remove Sendmail.