>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? Under the current setup, any domain that has an A record is presumed to be a mail domain, and if it's not, there's no good way to advertise that fact. (Current crocks include running a stub server that rejects everything, and the MX 0 . proposal.) In a world where the fraction of mail that is spam is 95% and growing, the load from unwanted mail to non-mail domains is significant. I have at least one host name that was never a mail domain, but since it used to appear in usenet headers it gets over 30,000 spams a day, every day. As Keith recently pointed out, since it is no longer 1983, the vast majority of names with A records are not mail servers nor are they domains that occur in mail addresses. They're workstations or PCs whose users get their mail through a domain and a server somewhere else. Or with IPv6, they'll be toasters and doorbells, even less likely to be mail servers. Getting rid of the AAAA fallback flips the default to be in line with reality -- most hosts don't want to receive mail directly, so if you're one of the minority that actually does, you affirmatively publish an MX to say so. R's, John _______________________________________________ IETF mailing list IETF@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf