"I have design a mail server in Ubuntu, its working but the problem is that i want to make 'id' into this mail server without being root user, how i can do it?"
Create a system user that will have rights/access to your mail server then he can create user id in mail server as you want.
"i am not able to access my mail server from other system(computer), how i can do it?"
You have to check connectivity within your local machine and your server by following methods
telnet mailserver iphostname 25
It shows connectivity for mail port
It also show connectivity between local machine and server in details.
Let me know if any help.
ESDS - Microsoft Dynamics ERP Partner