The above lines configure Postfix to relay mail through yoursmptserver.com on a specific port, telling it to authenticate and where to find the username and password. The last three lines specify the authentication types supported, where the certificate-authority-file is and that it should use TLS.
2. Define Username and Password:
a. Populate the sasl_passwd file. Create the file /etc/postfix/sasl_passwd with the following contents: