A New Internet-Draft is available from the on-line Internet-Drafts directories.
Abstract: «This document talks about SMTP operational experiences in IPv4/v6 dual stack environments. As IPv6-capable SMTP servers are deployed, it has become apparent that certain configurations of MX records are necessary for stable dual-stack (IPv4 and IPv6) SMTP operation. This document clarifies the problems that exist in the transition period between IPv4 SMTP and IPv6 SMTP. It also defines operational requirements for stable IPv4/v6 SMTP operation.»
http://www.ietf.org/internet-drafts/draft-motonori-dualstack-smtp-requirement-00.txt