This is simple. Postfix native IPv6 support was introduced in Version 2.2, which was released around the year 2005. So unless you are running an extremely outdated operating system, your Postfix MTA will be ready for IPv6. (Original Postfix IPv6 docs are here.)
The changes required to the Postfix main.cf are extremely basic:
# Tell Postfix to use IPv6:
inet_protocols = ipv4,ipv6
# Add the equivalents to your existing IPv4 setup to mynetworks
mynetworks = 127.0.0.1/32 1.2.3.0/24 [::1]/128 [2001:db8:dead:beef::]/64
# This will be required if you need to override an autoconfed address
# (for outbound connections):
smtp_bind_address6=2001:db8:dead:beef::deca:fbad
After this, stop and start Postfix. A postfix reload alone will not bind to the new IPv6 interface.
After local testing, set up an additional AAAA record for your mailexchanger:
MX 10 mx.example.com.
mx A 1.2.3.2
; The new record:
mx AAAA 2001:db8:dead:beef::deca:fbad
Don’t forget that you must, as always, set up proper forward and reverse DNS for your MX. Implement this at the same risk as if you were moving to a new IPv4 address.
Not long after the AAAA record is in place, you should see the spambots trying to deliver mail via IPv6, and Postfix will start to use IPv6 for outbound e-mail automatically if it can find a remote IPv6 MX. Which will be the case rather sooner than later.
See? You may still be an early adopter now, but you surely aren’t a pioneer living on the most remote corner of the net. I, for one, now have customers who use proper IPv6 e-mail without even knowing. đ
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