Qmail IPv6
Adding IPv6 support to qmail can be a daunting task. A modern qmail system includes several different components, with various patches and configuration options for each. There are a few patches on the internet that claim to add IPv6 support for a specific component, but I had trouble finding patches for every piece of my qmail install.
I’m not trying to defend IPv6. I realize there are many people with strong feelings towards the subject, including qmail’s author. Switching to IPv6 is a monumental task. It may never happen, but something needs to – we can’t keep NATing forever.
Many software projects have already added support for IPv6. My Gentoo box has been on an IPv6 network, via Hurricane Electric’s free tunnel broker service for a while now. Mac OS X has support for IPv6, as do the latest versions of Windows. Even Windows XP can support IPv6 if enabled. Postfix, Exim, and Sendmail all support IPv6.
In this series of posts, I will outline the steps I took to add IPv6 support to qmail. I use John Simpson’s combined patch for qmail as well as many other tools and methodologies described on his site, however many of the patches and instructions in these posts will work for other versions of qmail as well.
Components
John Simpson has an excellent illustration of a typical qmail system, Anatomy of a typical qmail system [PDF], on his website. The following articles describe the steps I took to enable IPv6 for each of the necessary components:
For Gentoo users, the patches described in each of the above posts can be installed automatically using the ebuilds in my gentoo-overlay. For others, I’ve listed all the IPv6 patches on my qmail patches page.
Testing
Testing your IPv6 enabled qmail setup can be a little confusing. There aren’t that many IPv6 enabled mail servers out there. Even worse, most people don’t have IPv6 connections.
Hurricane Electric provides a free IPv6 tunnel broker service that will allocate a /64 block of addresses that you can use. I host my personal mail server on a Linode which, despite being an excellent VPS, doesn’t have native IPv6. To get around this I set up a tunnel broker and enabled AAAA entries in DNS.
To test my setup, I had to install two separate qmail installs on different servers. Email addresses on my bltweb.net domain are now IPv6 enabled. If you’d like to use them to test, feel free to shoot me an email. Perhaps one day I’ll set up some type of reflector to automatically test.
IPv6 email experience
I’ve been running IPv6 mail servers at home and work for a few months now. I haven’t been keeping detailed statistics, but for the most part the only connections I’ve seen over IPv6 thus far have been spam 
Still, enabling IPv6 in qmail wasn’t as hard as I thought it was going to be, thanks to the pre-existing patches on the internet. Hopefully more and more companies will start to enable IPv6 on their networks, such as Netflix. While email may still be even further out it never hurts to be ready.
Hopefully these posts have helped you add IPv6 support to your qmail install. Feel free to leave comments or questions below and I’ll do my best to address them.
Excellent page. I have been looking for a Qmail/IPv6 solution for years.
Good man!