Postfix: What is the meaning of the non-loopback IPv6 addresses in the default value of mynetworks configuration parameter?

ARX asked:

On Postfix 3.1.0, postconf -d mynetworks prints:

mynetworks = [::1]/128 [fd6f:721b:f2ec::]/64 [fe80::]/64

What do the last two elements in the list, [fd6f:721b:f2ec::]/64 [fe80::]/64 represent? They are not loopback addresses. Are they private address space? Any specification reference available?

My answer:

The IP address range fe80::/64 is the link-local address range.

The IP address range fd6f:721b:f2ec::/64 is a subnet in the unique local address range.

Note that this configuration is not what is actually in the postfix file, but is the end result of configuring postfix. It is listening to all interfaces and networks in your configuration, and this line represents all of the networks configured on your host’s interfaces.

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