Arnt Gulbrandsen wrote:
Adding IPv6 support to internet mail forces a question: If there isn't
an MX RR for a given domain, does the SMTP client fall back to looking
up an A RR, A or AAAA, or A and AAAA? We have to choose, and all of them
represent a change.
Look up either A or AAAA: A-only hosts would look up A, AAAA-only hosts
would look up AAAA, dual-protocol hosts would look up both, and an
address would be deliverable or not depending on who's sending.
Basically, the current task is one of supporting a dual-stack networking
environment. That's a challenge for all Internet use, not just email.
Solutions for it need to be universal, not specific to email.
The SMTP specification should be modified in the smallest and most localized
fashion possible and particularly should not make any changes to its
A rather simple and straightforward task that the current draft
satisfies reasonably, modulo the usual wordsmith-hacking.
I read the -06 draft as permitting the last two alternatives ("A or
AAAA", "A and AAAA"). 2821 itself says A.
It appears that there has been a spontaneous desire for some spiffy
new goals to be overloaded onto that one, long-standing *requirement*.
This amounts to retro-active re-design on-the-fly.
We can't escape redesigning this. IPv6 forces us to.
v6 forces adding v6 address records. It does not force changing the