yum install postfix on fedora
you will need to get
yum install redhat-switch-mail
then run
/usr/sbin/redhat-switch-mail
and switch it over to postfix (or exim if your using that).
You can follow this howto here: http://www.fedora.us/wiki/SwitchingToPostfix
And there is also another mysql/postfix one here: http://www.fedora.us/wiki/PostfixWithMySQL