If you get message “qmailadmin was not found on this server” while browsing qmailadmin then it must be something with script alias. add this in your httpd.conf and restart the service

ScriptAlias /cgi-bin/ “/usr/lib/cgi-bin/”

<Directory “/usr/lib/cgi-bin”>
AllowOverride None
Options None
Order allow,deny
Allow from all
</Directory>