The Postfix configuration procedure is as below: The configuration files main-cf and master-cf are found in /etc/postfix folder. We can find where these files are located as shown below. Please find the master.cf and main.cf files, and make the configurations as are present in these files main-cf master-cf By default, Postfix will forward mail from clients in authorized network blocks to any destination. Authorized networks are defined with the mynetworks configuration parameter. Many Virtual Machines can be relayed to an SMTP Server. For that the private IP's of these VMs need to be specified in the mynetworks configuration parameter in main.cf file. In main.cf file edit the mynetworks parameter with the list of IPs of the VMs that uses the SMTP Server as a mailing Server. Specify the IP address of the machine in CIDR (network/mask) notation or simpl...