In this section we're going to discuss what you have to do to install Postfix on your system.
Postfix does have some prerequisites to installation. Probably the most significant of these is that sendmail must not be installed. so we'll start by getting sendmail off of your system. When you try to install Postfix with sendmail installed you will see this:
[root@ntbox /root]# rpm -Uvh postfix-19990906_pl06-1.i586.rpm error: failed dependencies: sendmail conflicts with postfix-19990906_pl06-1
So in order to fix this we would have to remove sendmail. It's important to note that it is *NOT* a good idea to force this install as there is a very real conflict between the sendmail binary and Postfix' version of the same. In short, just say no.
So now we need to remove sendmail. This is quite simply done using RPM but there are a couple of things which should be done first.