You can configuring Postfix MTA to use as a Smarthost i.e. routing all mails to a smarthost. A smarthost can be an external smtpd server provided by SendGrid, AWS, Rackspace, Google apps/Gmail, ISP or your own server in another data center. In this tutorial, you will learn how to install a Postfix smtpd and send email through ISP/Google Apps/SendGrid/AWS/Rackspace cloud email services with the help of the relay server.