> On Tue, 15 Jan 2008, Mark Andrews wrote: > > > > Since there is no [MX] fallback to AAAA > > Wrong. http://www1.ietf.org/mail-archive/web/ietf/current/msg49841.html > > Tony. Since when has Informational been equivalent to Standard? Synthesizing a MX record on NODATA to a MX lookup or a subsequent AAAA lookup is bad engineering decision. It will work reasonably well for IPv4 only + dual stack envirionment. It will not work will for IPv4 only + dual stack + IPv6 only envirionment. The reason it is a bad engineering decision is that: * the IPv4 only world needs a MX to find a dual stack MTA to relay into the IPv6 network. * the IPv6 world has a raft of solutions which will allow it to initiate a connection to a IPv4 only MTA without having to find a dual stack MX for the mail domain. * it changes the definition of what it means to exist in the mail domain and you will have different MTA's making different existance decisions. Some will say that AAAA + no MX exist but others will say that the site does not exist. Do you really thing we should be trying to force a upgrade of all MTA's on the planet to support MX synthesis from AAAA when there is no engineering need to to this? MX from A was a transition strategy. IPv6 only sites have a transition strategy that doesn't require synthesis. It is advertise a dual stack MX. At some point in the future sites will stop having a dual stack MX, the same way they stopped adding A records for mail only domains back in the 90's. Mark -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews@xxxxxxx _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf