On Tue, Apr 01, 2008 at 02:08:54PM -0700, Dave Crocker wrote:
One could say, "Anything that eliminates the use of an A RR as a
substitute registration changes this flexibility."
What this reformulation misses is that using an A* record means that there
is no incremental registration requirement. Since the A* record is there
for other reasons, it means that being an email server only requires
running the software.
That is how it was, decades ago. And it made sense, in a time when
computers had to be moved by a large number of trucks.
Then MX records were invented, and this fall back came into existence.
That too made sense at the time. From that moment on, an *A* record
would also function as a default MX record.
But this does not imply an *AAAA* record needs to. And even if it
did, things change.
One of the reasons for IPv6 was a large number of possible addresses,
so that each person could have their own range, and make it possible
to give your wrist watch an address. It is unlikely that all of such
new devices will receive mail.
Compare:
Most devices on the net can receive mail
vs.
Most devices on the net cannot receive mail
So the requirement "How should the intent to receive email for a
domain be signaled?" is, in fact, a very basic change to the core
Internet mail service model.
Funny, I thought it was a question.
There is currently no requirement to register intent. So to ask the
question is to look for a change to the model.
If the intention was "no change", then IPv6 would have been exactly
like IPv4 but just with larger addresses. It isn't.
The world has changed, and that includes SMTP. There is no reason to
implement an antique fall back mechanism into a brand new protocol.