One of the problems I have seen first-hand is "disappearing" mail. Example: A webserver sends outbound email directly, but doesn't want to receive inbound email. The hostname leaks and mail gets sent to that address, based on the A(AAA) record. The mail is "received", but disappears into some never-seen /var file. In that case, the sender never suspects that anything is amiss; it would be much better if the sender got an immediate "sorry, that domain name doesn't support email service" error. Even if you turn off sendmail, as someone has pointed out earlier, the sending MTA will retry for several days until giving up, thus delaying error notification that would be immediate otherwise in this particular case. You can obviously turn off sendmail local delivery, but many of the standard web hosting (cPanel and kin, but also the standard RH mail setup) arrangements don't make it particularly easy to have outbound- only sendmail. Thus, disabling AAAA checking seems to provide much cleaner error behavior. The 'MX 0' proposals would achieve some of the same results, but removing the AAAA lookup is default-safe, rather than requiring operator action. It's too late to change the A behavior, but there doesn't seem to be a reason to perpetuate this violation of the principle of least surprise. Henning On Mar 29, 2008, at 10:34 AM, Theodore Tso wrote: > On Sat, Mar 29, 2008 at 10:16:10AM -0400, Keith Moore wrote: >> I think it is time to put an end to specious arguments. >> >> These standards get used for decades. I don't think it's >> appropriate to >> cripple them because of some arrangement that happens to exist now >> from >> a few dysfunctional DNS providers. Providers will get more >> flexible as >> the need becomes apparent, and domain owners who have problems with >> their DNS providers can change providers. It's not difficult. > > So I must be missing something, probably because I deleted without > reading closely enough one of the earlier messages on this thread. > But please indulge me --- exactly what is the benefit of deprecating > the "A" fallback, and/or not doing a lookup on the AAAA record if the > MX record doesn't exist? Is it the load on the nameservers that > people would believe would be reduced if we didn't do this? Is that > really a problem? Or is it something else? > > - Ted > _______________________________________________ > IETF mailing list > IETF@xxxxxxxx > https://www.ietf.org/mailman/listinfo/ietf _______________________________________________ IETF mailing list IETF@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf