Below are snippets for the settings you can use to enable IPv6 on Postfix. These settings can be changed/added from /etc/postfix/main.cf

Select the protocols which postfix uses:

  • inet_protocols = ipv4
  • (DEFAULT: enable IPv4 only)

  • inet_protocols = all
  • (enable IPv4, and IPv6 if supported)

  • inet_protocols = ipv4, ipv6
  • (enable both IPv4 and IPv6)

  • inet_protocols = ipv6
  • (enable IPv6 only)

    Set the listen interface:

  • inet_interfaces = all
  • (DEFAULT, all IPv4 and IPv6 interfaces available)

  • inet_interfaces = loopback-only
  • (Postfix version 2.2 and later)

  • inet_interfaces = 127.0.0.1
  • (Just Localhost)

  • inet_interfaces = 127.0.0.1, [::1]
  • (Postfix version 2.2 and later)

  • inet_interfaces = 192.168.1.2, 127.0.0.1
  • (Multiple IPv4)

  • inet_interfaces = [2001:db8::dddd:eeee:ffff], [2001:db8:42:1af::1]
  • (Postfix version 2.2 and later)

    You can also set the preferred SMTP IP to be used.

  • smtp_bind_address6 = 2001:db8:42:1af::1
  •  
     

    Source and more information: http://www.postfix.org/IPV6_README.html