Install and Configure Mail Server on Linux System

Mail Transfer Agent
A Mail Transfer Agent (MTA) is the program which receives and sends out the email from your server, and is therefore the key part. The default MTA in Ubuntu is Postfix, but exim4 is also fully supported and in the main repository.
Postfix - this guide explains how to set up Postfix.

In order to install Postfix with SMTP-AUTH and TLS, first install the postfix package from the Main repository using your favorite package manager. For example:
sudo aptitude install postfix


Configuration
From a terminal prompt:
sudo dpkg-reconfigure postfix
Insert the following details when asked (replacing server1.example.com with your domain name if you have one):
General type of mail configuration: Internet Site
NONE doesn't appear to be requested in current config
System mail name: server1.example.com
Root and postmaster mail recipient: <admin_user_name>
Other destinations for mail: server1.example.com, example.com, localhost.example.com, localhost
Force synchronous updates on mail queue?: No
Local networks: 127.0.0.0/8
Yes doesn't appear to be requested in current config
Mailbox size limit (bytes): 0 
Local address extension character: + 
Internet protocols to use: all