Postfix mynetworks

[Richard Esplin]

In the default Postfix main.cf for Debian Lenny, the mynetworks line looks 
like this:

mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128

This is what I understand:
* The 127.0.0.0/8. It is classic CIDR IPv4 notation, which I am comfortable 
with.
* The rest is CIDR IPv6 notation.
* The :: is a group of zeros in an IPv6 address.
* The ::1/128 is the IPv6 loopback (thank you Wikipedia).
* IPv6 addresses need to be in brackets because the ":" is reserved for other 
config syntax (a common convention--not just Postfix, and not just because of 
the port identifier).

My question is:
* Why include ::ffff:127.0.0.0/104?

I thought about asking on #utah, but I want this in the plug archives. Then 
next time I ask this question, Google might help.

Thanks,

Richard