2.3. Configuring Postfix to forward all emails to a mail relay

Procedure

1. To prevent Postfix from accepting any local email delivery and making it a null client, edit the /etc/postfix/main.cf file and make the following changes:

   1. Configure Postfix to forward all email by setting the mydestination parameter equal to an empty value:

      mydestination =

      In this configuration the Postfix server is not a destination for any email and acts as a null client.

   2. Specify the mail relay server that receives the email from your null client:

      relayhost = [<ip_address_or_hostname>]

      The relay host is responsible for the mail delivery. Enclose <ip_address_or_hostname> in square brackets.

   3. Configure the Postfix mail server to listen only on the loopback interface for emails to deliver:

      inet_interfaces = loopback-only

   4. If you want Postfix to rewrite the sender domain of all outgoing emails to the company domain of your relay mail server, set:

      myorigin = relay.example.com

   5. To disable the local mail delivery, add the following directive at the end of the configuration file:

      local_transport = error: local delivery disabled

   6. Add the mynetworks parameter so that Postfix forwards email from the local system originating from the 127.0.0.0/8 IPv4 network and the [::1]/128 IPv6 network to the mail relay server:

      mynetworks = 127.0.0.0/8, [::1]/128

2. Verify if the Postfix configuration in the main.cf file is correct:

   # postfix check

3. Restart the postfix service to apply the changes:

   # systemctl restart postfix