Dear unspawn,
Below is the results of both commands you gave me. What does it means by sendmail.postfix? Which is the one is working postfix or sendmail?

Even though the package name should be clear from the link I said run 'rpm -qf' on the result like 'rpm -qf /usr/sbin/sendmail.postfix'.

Dear unspawn,
Ok I got it now.
So I am following this link now http://www.cyberciti.biz/tips/howto-...l-address.html. I could this
1.vi /etc/postfix/main.cf
2.smtp_generic_maps = hash:/etc/postfix/generic
3. here I am having problem tom-01@server01.hosting.com tom@domain.com? What is that server does not have a domain name? So what should I do then?

You can mask "root@localhost.localdomain" as a valid local account name. Note where it says "domain.com" you need to change it for a fully qualified domain name. This is the name that the IP address of your server resolves to (and it should have a reverse-resolvable address or PTR as well).

*Having watched your current three threads for some time now I have serious doubts about you running a Linux server. I suggest for the time being you halt Apache, MySQL, PHP, PHPMyAdmin and anything else you have installed like vBB, Wordpress, Joomla, etc, etc or whatever else accessible over the network and start reading the standard documentation Centos comes with especially the installation and administrators guide. At this stage you should not be exposing any services to the network except SSH (which you don't log into as root but as unprivileged user and using pubkey auth).

Dear unspawn,
I have been reading the documentation and from there I am testing each of the services and trying to harden it as much as possible with the help from you guys. I understand I am quite new to all this sorry for the inconvenience caused. So that is why I am taking those advices and trying it over one by one.