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

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