SMTP folks might want to look at this Internet-Draft:
A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Next Generation Transition Working Group of
the IETF.
Title : IPv6 SMTP operational requirements
Author(s) : M. Nakamura, J. Hagino
Filename : draft-ietf-ngtrans-ipv6-smtp-requirement-01.txt
Pages : 6
Date : 05-Jul-01
The memo lists operational requirements for IPv6 SMTP, and IPv6-capable
MX DNS records. As we deploy IPv6 SMTP servers, it became apparent that
we need certain configuration in IPv6-capable MX DNS record, for stable
dual-stack (IPv4 and IPv6) SMTP operations. The document tries to
clarify the problems we have in transition period between IPv4 SMTP and
IPv6 SMTP, and operational requirements for stable IPv4/v6 SMTP
operation.
A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-ngtrans-ipv6-smtp-requirement-01.txt