it gives feature to send mail anonymously or with authentication depending upon out host.
Suppose that you want to send a fake email to lightningbolt@try.com.
Firstly, using "nslookup" command to find the exchange server of "try.com" (set type=mx)
dig mx try.com
Coz SMTP protocol doesn't authorize on exchange server, you can directly send MIME format E-mail to the exchange server.
Tips: Testing it on your own email to make sure your E-mail won't be sent to Trash.