A smart host is a type of mail relay server which allows an SMTP server to route e-mail to an intermediate mail server rather than directly to the recipient’s server. [Wikipedia]
This document aims to describe some simple steps to setup a Postfix eMail server with a SmartHost used to relay messages through. The SmartHost will be authenticated and secured trough TLS.
1. Create a password file in /etc/postfix/relay_password containing SMTP host, username and password (used for submission authentication) as shown: