Yep, I think there was a post about setting up IPv6 correctly on HN a while back. Alternatively, you can make your host not respond to IPv6 at all.
If I remember correctly, the problem isn't that IPv6 needs to be set up, but that if your host listens on IPv6, Google will default to that and then your SPF/DMARC/DKIM setup needs to work with IPv6. If you don't have an external IPv6 address, then you don't need to configure SPF etc... for IPv6 and you should be fine.
If I remember correctly, the problem isn't that IPv6 needs to be set up, but that if your host listens on IPv6, Google will default to that and then your SPF/DMARC/DKIM setup needs to work with IPv6. If you don't have an external IPv6 address, then you don't need to configure SPF etc... for IPv6 and you should be fine.