Install Postfix server "sudo aptitude install postfix" and input these options:
Mail Server Configuration -> Internet Site
System Mail Name -> smartonline.com
Root and postmaster mail recipient -> sysadmin
Other destinations to accept mail for (blank for none) -> localhost
Force synchronous updates on mail queue? -> No
Local networks -> 172.16.110.0/8, 127.0.0.0/8
Mailbox size limit (bytes) -> 0
Local address extension character -> BLANK
Internet protocols to use -> ipv4
If you want to reconfigure the postfix, execute "sudo dpkg-reconfigure postfix".
Testing Mail
telnet <IP> 25
EHLO
MAIL FROM: <from-email>
RCPT TO: <recipient-email>
DATA
Type message here.
. <Enter>
The last line leaves DATA mode.