[CentOS] CentOS 5 and removing sendmail

Hi, I want to build a spam gateway for my mail server using postfix. I issued an rpm -e sendmail and got the following output:

# rpm -e sendmail
error: Failed dependencies:
        /usr/sbin/sendmail is needed by (installed) redhat-lsb-3.1-12.2.EL.el5.centos.i386
        smtpdaemon is needed by (installed) mutt-1.4.2.2-3.el5.i386
        smtpdaemon is needed by (installed) fetchmail-6.3.6-1.el5.i386
        smtpdaemon is needed by (installed) mdadm-2.5.4-3.el5.i386

How does one replace sendmail with postfix (I am hoping to install from source using the latest version)?

Thanks!
jlc
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