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Re: not delivering, and History of fallback to A

2008-03-30 09:59:01

This also ignores the issue of what is the right thing to do in the
transitional case where there's no MX record but a mixture of A and AAAA
records. Only falling back to the A record subset seems, well, wrong.

Well, gee, that's what happens right now. The question is where we go from here.

[... that] doesn't seem like much of an argument compared to the advantages laid out in my last message of having hosts default to not being mail servers.

I assume you're referring to the problem of mail sitting in the queues waitinfg
to be delivered to a system that's never going to accept it. I'm afraid I don't
buy your reasoning on this one either.

10 years or so ago this used to be a real issue - we used to get customer
complaints  all the time about stuck mail to some router, or to lab PCs, or

The mail sitting in the queues isn't the problem, it's the load on all of the hosts that the bogus mail is hammering on. Remember my non-mail host with the 30,000 spams per day. Those aren't just attempts, by the way, I set up an MTA and collect 30,000 actual spams. I tried soft failing and the load was somewhat more.

The lack of complaints is probably because we no longer run versions of sendmail that report back every two hours to say that your message hasn't bounced yet. Most bounces these days are spam blowback, which tells me that if the user doesn't see a failure report really soon while he still remembers sending the message, it'll be lost in the noise.

Speaking of lost in the noise, one thing that's really different from 25 years ago is that reliable mail depends as much on not delivering spam as it depends on delivering the real mail. I don't know how many of the other people in the conversation see the feedback reports when people at AOL, Hotmail, and other large ISPs hit the spam button on your users' mail, but if you can arrange to see them, do so, because it's a real eye opener. A message that is hidden in a mailbox full of spam is lost as thoroughly as one that was never delivered. I cannot tell you how many spam reports I get for utterly unobjectionable mail that was clearly scooped up with a hundred other messages and reported en masse. I've had to tell people on my church's mailing list that no, I can't keep putting you back on the list if you keep reporting it as spam. So with that in mind, even if something makes it a little harder for the least competent to set up their mail servers, that's OK if will tend to improve mail reliability overall.

With respect to DNS setup, I spend a certain amount of time helping people fix their SPF records. (Not because SPF is a good idea, but because it's hard to get mail into Hotmail if you don't.) I see a fair number of DNS management control panels, and I don't recall seeing any that made MXes hard to set up. Maybe they exist, but I'd be surprised if they were any more common than any other random DNS breakage.



So I believe the correct course going forward is to have the same fallback
rules for AAAA that we do for A. Having said all this, it certainly isn't a
showstopper for me if this goes the other way

I can live with the current ambiguous language, particularly if we agree that we need to have some way to declare in the DNS that a name accepts no mail, be it no default to AAAA, MX . or whatever.