I wanted to learn Mail Servers, since i don't have a VPS, i am trying to work with postfix in my LAN env.

I have 2 Virtual Machines running Cent OS with postfix installed.

I have changed there hostnames with hostname command and here are the details :-

server.test.com ( 192.168.2.2 )
client.test.com (192.168.2.4 )

In the /etc/host file of server , i have made an entry of client.test.com 192.168.2.4 and same with client side for server.

Now is this configuration right ? What am i suppose to do if i want to send mail to client.test.com from server.test.com ?

If there is root account in client side, should i send mail to root@client.test.com from server ?

You can't properly test Internet mail functionality using hosts files alone; you'll have to set up a local DNS server (I recommend BIND). Sure, you could force the mail client software to use the Postfix server for all outgoing mail, but why not configure the test environment the same the way Internet domains and mail servers are configured?

Mail is delivered to the SMTP server defined as the Mail Exchanger for a given domain. This definition is found in a particular kind of DNS record, the MX record, in the DNS zone file for every mail-enabled domain.

You could to do something like this:

1. Install the BIND DNS server (it may already be present on your system
2. Create a DNS zone for testing purposes (you should use an invalid TLD, like "mailtest.local")
3. Create an A record in this zone (something like "mail.mailtest.local"), pointing to the IP address of the mail server
4. Create an MX record pointing to the name of the A record from [3]
5. Configure forwarding so the BIND server can resolve Internet names as well
6. Edit /etc/resolv.conf on both systems to have them use this DNS server

You should then be able to send mail from the client host to the server, and you should proceed to edit the Postfix configuration file in order to have it accept mail for the "mailtest.local" domain.