I recently embarked on a mission to make Qmail work with IPv6. I succeeded, in part, with the qmail-jms1 patched version of qmail. Overall, however, I was not completely happy with the jms1 approach. The author of this patch had added some slightly unusual functionality and most importantly this patch did does not appear to be compatible with the qmail-spp patch, which I used to perform valid user checks before accepting mail.
Recently. however, I discovered Qsmtp (http://opensource.sf-tec.de/Qsmtp/).
Qsmtp provides a drop in replacement for qmail-smtp and qmail-remote which provides advanced anti-spam features like SPF, DNS RBL, MAIL FROM validation, vpopmail user validation and more.
It also provides full IPv6 support.
For a Gentoo system, it’s as simple as adding the author’s overlay in layman and emerging netmail-Qsmtp.
This seems to work flawlessly. I’m impressed.