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Spam Networking IT

Fight Spam With Nolisting 410

An anonymous reader writes with the technique of Nolisting, which fights spam by specifying a primary MX that is always unavailable. The page is an extensive FAQ and how-to guide that addressed the objections I immediately came up with. From the article: "It has been observed that when a domain has both a primary (high priority, low number) and a secondary (low priority, high number) MX record configured in DNS, overall SMTP connections will decrease when the primary MX is unavailable. This decrease is unexpected because RFC 2821 (Simple Mail Transfer Protocol) specifies that a client MUST try and retry each MX address in order, and SHOULD try at least two addresses. It turns out that nearly all violators of this specification exist for the purpose of sending spam or viruses. Nolisting takes advantage of this behavior by configuring a domain's primary MX record to use an IP address that does not have an active service listening on SMTP port 25. RFC-compliant clients will retry delivery to the secondary MX, which is configured to serve the role normally performed by the primary MX)."
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Fight Spam With Nolisting

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  • Oblig. (Score:5, Insightful)

    by Whiney Mac Fanboy ( 963289 ) * <> on Monday January 22, 2007 @11:09PM (#17719106) Homepage Journal
    YASIGFINFE (Yet Another Spam Idea Good For Individuals, Not For Everyone) - Spammers will change their techniques to be more RFC compliant as soon as (if) Yahoo, AOL, Hotmail, Gmail adopted this method.

    Your post advocates a

    (x) technical ( ) legislative ( ) market-based ( ) vigilante

    approach to fighting spam. Your idea will not work. Here is why it won't work. (One or more of the following may apply to your particular idea, and it may have other flaws which used to vary from state to state before a bad federal law was passed.)

    ( ) Spammers can easily use it to harvest email addresses
    ( ) Mailing lists and other legitimate email uses would be affected
    ( ) No one will be able to find the guy or collect the money
    ( ) It is defenseless against brute force attacks
    (x) It will stop spam for two weeks and then we'll be stuck with it
    ( ) Users of email will not put up with it
    ( ) Microsoft will not put up with it
    ( ) The police will not put up with it
    ( ) Requires too much cooperation from spammers
    ( ) Requires immediate total cooperation from everybody at once
    (X) Many email users cannot afford to lose business or alienate potential employers
    ( ) Spammers don't care about invalid addresses in their lists
    ( ) Anyone could anonymously destroy anyone else's career or business

    Specifically, your plan fails to account for

    ( ) Laws expressly prohibiting it
    ( ) Lack of centrally controlling authority for email
    ( ) Open relays in foreign countries
    ( ) Ease of searching tiny alphanumeric address space of all email addresses
    (x) Asshats
    ( ) Jurisdictional problems
    ( ) Unpopularity of weird new taxes
    ( ) Public reluctance to accept weird new forms of money
    ( ) Huge existing software investment in SMTP
    ( ) Susceptibility of protocols other than SMTP to attack
    ( ) Willingness of users to install OS patches received by email
    ( ) Armies of worm riddled broadband-connected Windows boxes
    (X) Eternal arms race involved in all filtering approaches
    ( ) Extreme profitability of spam
    ( ) Joe jobs and/or identity theft
    ( ) Technically illiterate politicians
    ( ) Extreme stupidity on the part of people who do business with spammers
    (x) Dishonesty on the part of spammers themselves
    ( ) Bandwidth costs that are unaffected by client filtering
    ( ) Outlook

    and the following philosophical objections may also apply:

    ( ) Ideas similar to yours are easy to come up with, yet none have ever
    been shown practical
    ( ) Any scheme based on opt-out is unacceptable
    ( ) SMTP headers should not be the subject of legislation
    ( ) Blacklists suck
    ( ) Whitelists suck
    ( ) We should be able to talk about Viagra without being censored
    ( ) Countermeasures should not involve wire fraud or credit card fraud
    ( ) Countermeasures should not involve sabotage of public networks
    ( ) Countermeasures must work if phased in gradually
    ( ) Sending email should be free
    ( ) Why should we have to trust you and your servers?
    ( ) Incompatiblity with open source or open source licenses
    ( ) Feel-good measures do nothing to solve the problem
    ( ) Temporary/one-time email addresses are cumbersome
    ( ) I don't want the government reading my email
    ( ) Killing them that way is not slow and painful enough

    Furthermore, this is what I think about you:

    (x) Sorry dude, but I don't think it would work.
    ( ) This is a stupid idea, and you're a stupid person for suggesting it.
    ( ) Nice try, assh0le! I'm going to find out where you live and burn your
    house down!
    • Re:Oblig. (Score:4, Insightful)

      by um... Lucas ( 13147 ) on Monday January 22, 2007 @11:15PM (#17719150) Journal
      If i had mod points, I'd say you were insightful... Instead, I can only chime in, agree and say "well, now that those instructions are posted, surely it'll just be a day or a week until spammers work around that. So, nice idea, not much of a future, I don't think...
      • Re:Oblig. (Score:4, Interesting)

        by arivanov ( 12034 ) on Tuesday January 23, 2007 @03:21AM (#17720636) Homepage
        That is besides the article being absolute and utter bollocks as far how and why you do this.

        First, at least some botnets will hit secondary MX-es first. The reason for this is because one person too many out there think that the secondary MX gets invoked only when the first one fails and do not put full sets of antispam software on it.

        Second, as far as detecting SPAM is concerned the fact that a system has tried your first MX is valuable information. So while the first MX may not accept the message it should still be available to record the attempt. As a result, if you have multiple level different priority MX-es you can vastly improve on standard greylisting. The first MX resets with the usual "greylisted for 300 seconds, come again". After that system expects that you appear on the second, third, etc in the correct order and try on all MX-es of equal value before going up. In other words your connection pattern should follow the one of a normal MTA. Zombie writers are too lazy to do that (and that takes too much resources as far as they are concerned) so they fail the test and get their greylist timeout pushed up. Normal MTAs get their greylist timeout adjusted down and may even be allowed in on one of the last MX-es. I have done that using exim/mysql and I know a few other people who do that as well (trivial actually). In fact, looking at my mail logs it looks like yahoo does something similar for receiving mail and I can bet that they are not the only ones.

    • Re:Oblig. (Score:5, Interesting)

      by AchiIIe ( 974900 ) on Monday January 22, 2007 @11:21PM (#17719206)
      in response to:
      > (x) It will stop spam for two weeks and then we'll be stuck with it

      There is another anti spam technology called (doubleverify?), if a message smells like spam the smtp server rejects it saying unavailable and waits for the sender to send it again (an hour or so later). For people who use it it works fine, but people who use it are in the minority, thus spammers won't bother writing new systems that keep track of what was rejected etc. They appeal to the (cheap) masses.

      Same here, unless this becomes widely popular few spammers will adopt it. Thus there's a chance for this to work (hopefully, unlike doubleverify this is not patented)
      • if a message smells like spam the smtp server rejects it saying unavailable and waits for the sender to send it again (an hour or so later).

        Great. Lots of emails delayed for an hour, lots of emails lost due to non-rfc compliant sender. Doubleverify are welcome to the patent on that utterly useless (in the real world) idea.
        • Re: (Score:3, Insightful)

          by Carewolf ( 581105 )
          Very stupid and very annoying idea!

          It fails to account for the fact that spammers use fake FROM-addresses, and stupid &%@! SMTP servers bounce the email to the fake FROM-address. I receive around 10000 bounced spam-emails per day of this type because one spammer somewhere decided to use my domain as a fake FROM-address.

          Just discard the email. Don't bounce!
          • Re:Oblig. (Score:5, Insightful)

            by ArsenneLupin ( 766289 ) on Tuesday January 23, 2007 @07:22AM (#17721656)

            Just discard the email. Don't bounce!
            "Great" piece of advice. That way, in case of a false positive, the sender gets no warning that something is amiss.

            Mail should not be silently discarded (except in the most extreme circumstances). Reject it. Rejecting a mail means that the receiving MTA returns an error code (in the 5xx range) to the sending MTA, so that the sending MTA may bounce (which it won't do if it is a zombie, so no scatterback).

          • Re: (Score:3, Informative)

            by raju1kabir ( 251972 )

            Very stupid and very annoying idea! It fails to account for the fact that spammers use fake FROM-addresses, and stupid &%@! SMTP servers bounce the email to the fake FROM-address. I receive around 10000 bounced spam-emails per day of this type because one spammer somewhere decided to use my domain as a fake FROM-address. Just discard the email. Don't bounce!

            How did this get marked insightful? Sending a temporary failure SMTP response code is not a bounce, and should not result in the generation of a

      • by khasim ( 1285 ) <> on Monday January 22, 2007 @11:33PM (#17719308)
        "Greylisting" is where an SMTP server refuses messages for a certain amount of time. You set the criteria on why the message would be refused and how long the server would refuse to accept it.

        It's been pretty much defeated now because so many spammers have their machines try to hammer the message through until it does go through.

        I'm using greylisting right now and the only advantage is that many times a spammer will end up on an RBL during the 15 minutes that I'm refusing his messages.

        Remember, the spammers have, effectively, unlimted bandwidth and unlimited processing power at their disposal.
        • by Anonymous Coward on Tuesday January 23, 2007 @12:21AM (#17719664)
          Just an aside on greylisting: I run a large mail server and we WERE using greylisting. However we have found that many firewalls and anti-spam appliances that act as email proxies cannot respond to the 451 or 421 "try again" response used by greylisting. The appliances bounce the message back to the sender reporting it as a server failure. Unfortunately, this user group includes an ever growing number of goverment agencies and public schools. My best guess is that these appliances have no way to store the message should the first attempt at delivery fail.

          I sincerely doubt that most of them would ever try more than the primary MX when delivering mail either.

          Non-complience with the standards by email handling programs just makes it easier for the spammers by taking away a postmasters anti-spam tools :-(
          • by Dion ( 10186 ) on Tuesday January 23, 2007 @02:58AM (#17720540) Homepage
            Well, you can solve this by whitelisting the broken appliances.

            A better solution would be to ignore the problem, because those appliances are broken and need to be replaced or fixed no matter what.

          • by pe1chl ( 90186 ) on Tuesday January 23, 2007 @04:17AM (#17720882)
            Firewalls and anti-spam appliances have often very broken SMTP implementations, and not only do they have bad support (when you report it is broken, you get a "it works with most servers so it must be YOUR server that is broken!") but also when an update IS released, it can take years before it is installed by the users.

            However, I still believe that the best way to handle this situation is by not working around it. When users complain that a good fraction of their mail gets bounced for no apparent reason, there may be action. When you implement a workaround, things will remain as they are.

            This does not only affect greylisting. I have seen bad SMTP bugs in NAI's virus checker, "SurfControl E-mail Filter", "logsat spamfilter for ISP", and another spamfilter whose name I forgot. tried to issue bug reports via their support system. It often is near impossible to submit a bug report when you are not a user of their product, and once you get through they are completely uninterested when you are not Microsoft or Sendmail. Pointing them to the RFC does not work at all, they fix bugs by the "if it delivers mail then it must be OK" paradigm.
        • by AchiIIe ( 974900 ) on Tuesday January 23, 2007 @01:40AM (#17720184)
          It's not quite greylisting. Greylisting denies access to the smtp server, this technology reads the whole message, analyzes it, rejects it, and waits for a second `exact` copy.

          see: 11045587 []

          From the FAQ (

          DoubleVerify gets two chances to automatically identify mail. When mail arrives at our mail server the first time our server requests the sending mail server to send it a second time. Spammers rarely comply. Legitimate mail servers typically resend the mail about fifteen minutes later. Once OlympusNet receives mail the second time, it immediately delivers that mail and continues to immediately deliver mail from that sender. The DoubleVerify process works invisibly and is handled automatically by the mail servers.
        • by RazzleDazzle ( 442937 ) on Tuesday January 23, 2007 @02:06AM (#17720322) Journal

          Remember, the spammers have, effectively, unlimted bandwidth and unlimited processing power at their disposal.
          If the big companies started doing this [] with OpenBSD's spamd and generating public logs, we could get some seriously entertaining data I am sure.

          From the link...

          --snip log example--
          This spammer got stuck for 47 minutes. Current spamd sets its socket receive buffer size to one character, forcing the sender to send one TCP packet for each byte of data, even if its a non-compliant "dump and disconnect" mailer. Of course, the spammer nearly immediately tries to retransmit the spam. Repeatedly.

        • Re: (Score:3, Informative)

          by Dion ( 10186 )
          Funny, I've found that switching to greylisting has meant that I went from 50+ spams pr. day on one account to 0-2, with the norm being 0.

          The trick is that I don't just use greylisting, I use greylisting + spamtrap driven RBLs, so that once the greylisting period runs out the RBLs have a much greater chance of having been hit by the same spammer and thus they catch him.

          Grylisting on its was a temporary fix, but it makes spamtrap driven RBLs pretty much bulletproof.

          You could get pretty much the same result s
        • Re: (Score:3, Informative)

          by toonerh ( 518351 ) *
          Greylisting still DOES help a lot in 2007. The majority of "zombie" spambots don't bother to requeue the "soft", 4xx, errors; also zombies that relay through their ISP generate a more obvious fingerprint and finally, and perhaps most importantly, the 30 minutes to 1 hour delay allows DCC, Razor2 and other spam signature databases to register hits at the expense of non-greylisters.
        • Zero Spam is easy... (Score:4, Interesting)

          by Kent Recal ( 714863 ) on Tuesday January 23, 2007 @06:44AM (#17721446)
          I use qconfirm [] myself but there's also tmda [] and others.
          *If* you are serious about getting rid of the spam then just do it. The technical part is readily available.

          I deployed that almost a year ago and never looked back. I still see the occassional spam in a
          mailing list folder because those go through unfiltered for obvious reasons but I couldn't care less.
          My inbox has been spam-free since then and that's what matters.

          I don't quite get why people are still bothering with greylisting, spamassassin, razor, dcc, bayes and
          the ilk. I tried them all and they're more trouble than it's worth. You get false positives, false negatives,
          it's a stupid game that you can't win.
      • Re: (Score:3, Interesting)

        by stoanhart ( 876182 )
        Yes, this method is called grey-listing. We used it at an ISP that I used to work for. It cut out mail load from 30000 messages per day to about 500. We gave people the option to disable it, but few did, because it worked so well and no one ever mentioned any missing emails.

        Most e-mail servers resend within 15 minutes (usually like 5-10), so it doesn't cause for much delay. Besides, once an e-mail made it through, we would simply allow all future emails from the same sender to the same recipient for up
    • Yep Funny (Score:4, Funny)

      by keeboo ( 724305 ) on Monday January 22, 2007 @11:42PM (#17719376)
      Standard Smartass Form for Comments on SPAM

      1. Please select format:
      ( ) In soviet Russia .... you! Kind of joke
      (x) The same old form on spam subject we're tired to see here
      ( ) Some comment on female parts
      ( ) Suggesting you/slashdot_readers are virgins
      ( ) Will it run Linux?
      ( ) Cowboy Neal

      2. Are you:
      (x) Meant to be funny
      ( ) In a bad day, trolling
      (x) Being authoritative on this subject
      (x) Expecting to be modded up
      ( ) Agreeing with the news
      (x) Trying to piss over something people might think it's interesting or relevant

      3. Include "I'll be modded down for this but...."? (Y/N)

      Thank you for submitting your message to the Slashdot forum.
      Slashdot Quick'n'simple Form: The easy way to show people how smart your are!
    • Re: (Score:2, Funny)

      by Triode ( 127874 )
      You must be the fastest typist in the known universe...

      We will later have to google: how to type a three page long sarcastic remark in such
      time as to still be able to submit it to a /. posting and have it be first post.

      You are commended, but for what we have no idea.
      • Re: (Score:3, Informative)

        by scottv67 ( 731709 )
        You must be the fastest typist in the known universe...

        Whiney Mac Fanboy is a subscriber. They (subscribers) get to see the articles before us mortals. First post isn't hard when you can reply to the article before the article is available to the unwashed masses.
        • Uh, they can't reply until the article goes live. And they aren't given any information on when it goes live. So he had to sit there and hit refresh and drive up page views just like anyone else would.

          Sorry, that wasn't meant to be a rant.
      • Re: (Score:3, Insightful)

        by jfengel ( 409917 )
        He types that fast because he's mostly filling out a form. Here it is: []

        The point is that there aren't any truly novel, effective spam solutions waiting out there. Whatever it is they're suggesting, it's been thought of before, or something like it, and it's already been found wanting.

        We don't need to rewrite the objections from scratch, and can just re-tread the old ones by filling out the form. Somebody will fill out that form for EVERY anti-spam solution posted o
    • Address Book (Score:3, Interesting)

      by iendedi ( 687301 )
      How hard would it be for Yahoo, Google and other internet mail services to simply have two inboxes?

      One for mail addressed to someone in your mailbox.

      One for everyone else.

      90% of my spam problem would be solved by this simple recipe.
      • Do you mean mail sent from someone in your address book? Addressed to someone in your mailbox does not make sense for Yahoo and Google.

        For a domain not having the catch all enabled remove a huge amount of spam though.
        • Re:Address Book (Score:5, Interesting)

          by dgatwood ( 11270 ) on Tuesday January 23, 2007 @01:05AM (#17719978) Homepage Journal


          • in addressbook: goto NOTSPAM.
          • address present as envelope sender in any incoming mailbox: goto NOTSPAM
          • address present as recipient in any outgoing mailbox: goto NOTSPAM
          • address has ever been present as envelope sender in any incoming mailbox:
            • at least one of those messages was flagged as spam: goto SPAM
            • none were flagged as spam: goto NOTSPAM
          • goto SUSPECT
    • Uhm... I wouldn't be so quick on that.

      I'd say a great many of your check marks might have also been said about the "grey listing" technique. I have been using greylisting for a relatively short time (about two months) but the results have been more than remarkable. This technique certainly warrants a slightly better evaluation than the one you provided above.

      Greylisting works for exactly the same reasons this other technique purports -- by utilizing a standard of behavior that real mail servers are suppos
    • Re:Oblig. (Score:5, Insightful)

      by jon787 ( 512497 ) on Tuesday January 23, 2007 @12:11AM (#17719608) Homepage Journal
      Don't have numbers to back it up, but most things I read say that the Secondary MX is *more* likely to be targeted by spammers on the belief that fewer filters will be in place to prevent spam.

      Those statements could be refering to their use as open relays though.
      • Re: (Score:3, Interesting)

        by stu_coates ( 156061 )

        I do have the numbers to back this up... check out the stats at [] - this exploits the fact that some spammers target low priority MX hosts and then holds them in a tar pit for as long as they keep the connection open - 671 hours in one case.

        More of an explanation here [].

  • Temporary Solution (Score:5, Insightful)

    by PhotoGuy ( 189467 ) on Monday January 22, 2007 @11:15PM (#17719142) Homepage
    This strikes me as the ultimate in temporary solutions. If spam senders *tend* to use only the primary MX record, and people start fighting spam by listing bad primaries, won't the spam senders simply start using secondaries? It almost seems the only way that this approach might be valuable, is if it weren't publicized and posted on /., and one kept it to oneself :)
    • by TheSkyIsPurple ( 901118 ) on Monday January 22, 2007 @11:30PM (#17719288)
      It amuses be a bit. I have the ultimate in no listing for one of my domains. =-)

      I used to received about 6 million spams a day across 3 relays for this domain.
      I removed all MX records for the domain, and the hostnames have nothing to do with the domain (so A record lookups won't help), but 30 days later I still was receiving over 2 million spams a day. After about 6 months the number really started falling off.
      • by TheLink ( 130905 )
        How do you receive 2 million spams a day after 30 days with the domains off? You temporarily put them back on to check?

        If you are really no longer using those addresses for communications, you could use them as a spam canaries.

        Increase the spam "score" of any message that goes to those addresses. If it's multiple "unrelated" addresses then it's even more likely to be spam.

        The spammer has to somehow detect this or send more unique emails - which slows them down.

        • Re: (Score:3, Informative)

          The kept the IPs handy, not even bothering to check DNS.

          I handled other domains on the same servers, so I'd still see the requests come in
      • Re: (Score:3, Interesting)

        by adrianmonk ( 890071 )

        I removed all MX records for the domain, and the hostnames have nothing to do with the domain (so A record lookups won't help), but 30 days later I still was receiving over 2 million spams a day. After about 6 months the number really started falling off.

        It's not hard to think that spammers are probably keeping lists of IP addresses rather than DNS names. They don't care about correctness, so there is no need for them to try the correct SMTP server. Therefore, why bother with the overhead of DNS? Or

        • Re: (Score:3, Insightful)

          by Calinous ( 985536 )
          That is, assuming you really have those 254 IP addresses ready. And if you have a C-class just for yourself, you are filthy rich :)
      • Re: (Score:3, Interesting)

        by Megane ( 129182 )

        I've got a similar story. When a good local ISP got bought up by a crappy CLEC who ran it into the ground, I switched over to the ILEC's DSL offering. However, they never closed my e-mail account, so I kept reading from it. After a while they switched their authentication so that I had to log in as "" instead of just my user name, but it still accepted my password.

        Naturally, all I got was spam on that account. But then the CLEC dropped the old domain name, which got snatched up by an ISP

    • by khasim ( 1285 ) <> on Monday January 22, 2007 @11:38PM (#17719340)
      Spammers will often try secondary (and lower) MX's because there's a good chance that the anti-spam AND ANTI-VIRUS systems on those machines are weaker (read "outdated") than on the primary MX.

      The more machines you have to maintain, the more likely you are to focus your efforts on the most critical ones and just let the other slide. Spammers are happy to exploit this.
    • Re: (Score:2, Insightful)

      by httpdotcom ( 749192 )
      The interesting thing about the solution is that it will increase costs for the spammer. Their MTA's will either dump the original mail, as it is not configured to handle secondary MX records (non-RFC compliant sender) or it will spend the cycles that would normally be used sending other messages. While the bounces could be shuffled off to servers designed specifically for the purpose of fighting this approach, it is still a win against spammers, in the short term.
      • Re: (Score:3, Informative)

        by bigberk ( 547360 )

        The interesting thing about the solution is that it will increase costs for the spammer.
        Not quite, because spammers don't really pay for bandwidth. They steal the computing power and bandwidth from victims (virus infected machines) to set up botnets, and then leverage the stolen resources for their marketing business.
      • Re: (Score:3, Insightful)

        by ocbwilg ( 259828 )
        The interesting thing about the solution is that it will increase costs for the spammer. Their MTA's will either dump the original mail, as it is not configured to handle secondary MX records (non-RFC compliant sender) or it will spend the cycles that would normally be used sending other messages. While the bounces could be shuffled off to servers designed specifically for the purpose of fighting this approach, it is still a win against spammers, in the short term.

        Not only do most spammers not pay for ba
    • by Frogbert ( 589961 ) <{frogbert} {at} {}> on Monday January 22, 2007 @11:51PM (#17719452)
      Thats why we all have to keep wraps on this idea. Don't tell anyone. It's much like Usenet, don't talk about it and everyone in the know benefits.
    • by tdelaney ( 458893 ) on Tuesday January 23, 2007 @02:59AM (#17720550)
      If you'd bothered to RTFA (which I did a month or so ago) you would notice that the secondary server will only accept mail which was first rejected by the primary.

      This means that servers *must* be RFC-compliant to deliver mail to a no-listed server - they must try to deliver to servers in the published order, and must try at least two.

      The big advantage with no-listing is that if the sending server immediately tries the secondary after the primary fails, here is almost no delivery delay.

      The big disadvantage of course is that an RFC-compliant spammer gets almost no delay either.
  • by pyite ( 140350 ) on Monday January 22, 2007 @11:17PM (#17719166)
    This is not a long term solution.

    1) It's bad netiquette, and a lot of people don't like that, including myself and I'm sure many other administrators.
    2) It's an artificial "defense" that is easily circumvented because the rule is obvious. It's security through obscurity with the added suck that there is no obscurity.
    3) It's solving a symptom and not any of the actual problems (e.g. hosts being compromised to send spam).

    Thanks, but I'll pass.

    • Given that there is NO 100% true solution to the problem, things have to be done... or at least tried. Greylisting could be counted in the same numbers that fit the reasons you list above, but it works remarkably well.

      I'm sure you advocate murdering the spammers for their deeds... (I don't though I quietly hope to see headlines to that effect in the daily news) but expecting marketers to "follow ettiquette" ain't gonna happen. At all professional levels, the same basic abandon of moral and ethical standar
  • funny (Score:4, Funny)

    by User 956 ( 568564 ) on Monday January 22, 2007 @11:18PM (#17719172) Homepage
    An anonymous reader writes with the technique of Nolisting, which fights spam by specifying a primary MX that is always unavailable.

    Funny, I fight afternoon meeting schedulings in almost the same way. Just specify a primary time that's always unavailable.
    • by proverbialcow ( 177020 ) on Monday January 22, 2007 @11:41PM (#17719370) Journal
      Funny, I fight afternoon meeting schedulings in almost the same way. Just specify a primary time that's always unavailable.

      When I worked overnights, I had a similar system.

      Boss: We need to talk.
      Me: Great. What night would you like to come in?
      Boss: No, I mean you should stay late.
      Me: But you don't come in until 9, and my shift ends at 7.
      Boss: But it's important!
      Me: Why is it always about your needs. Your need to have a meeting. Your need to get a decent night's sleep. What about my need not to sit around for two hours on the clock waiting for you to show up, surfing the web, all the while getting paid one-and-a-half my regular pa...okay, fine, you win.

      Then, when I became the boss years later, I would always show up at the beginning of the night shift to talk to the employees, and then go to the bar. It made the employees feel noticed and made my superiors think I was motivated. Turns out my best defense against assholes like me is actually having been me.
  • by Gothmolly ( 148874 ) on Monday January 22, 2007 @11:18PM (#17719176)
    We get stuff directed at our secondary all the time, despite having a highly available primary. Why? Our secondary is listed at another domain - they do our backup in the case of disaster. I can only assume that spammers hit it thinking that its a 'back door' into the network, perhaps we don't have the same rigorous anti-spam measures there.

    Dumb idea. You're better sending all your domain mail to gmail, using their spam filtering, and then pulling it from there.
    • by chathamhouse ( 302679 ) on Monday January 22, 2007 @11:49PM (#17719434) Homepage
      I run a mail system that pushes ~3million messages per day. Not huge, not small.

      We have thousands of domains pointed to our mail servers and secondary MX servers. Looking at the long run stats, I'd be tempted to completely disregard this technique.

      When we take a primary down for maintenance, the secondaries and alternate primaries (same weight MX) see the load almost immediately.

      I second the opinion that if this has any effect, it's only for low volume applications, with few/one domain.

      We generally see more hits straight to the secondaries by spammers hoping for less rigorous checking. It would be interesting to profile IPs connecting to secondaries without being seen at the primary assuming a primary is always available - I bet that a very high percentage of these connections to secondaries could be viewed as spam.

      The problem remains that most tricks of this sort - including greylisting - are eventually circumvented by spammers once the trick gains critical mass. Lets not forget that there are a lot of broken, yet not open relay, mail servers out there. Good engineers and administrators quickly find that Jon Postel's words ring true with their customers "Be liberal in what you accept, and conservative in what you send." - don't let your RFC enforcing configuration be responsible for delaying/blocking the delivery of that big contract your PHB was waiting for!

      • by anakog ( 448790 ) <> on Tuesday January 23, 2007 @06:08AM (#17721262) Journal

        I run a fairly low-key server, which I only use for my family, so I am not sure how relevant my data is.

        I remember at one point last year checking on the usage my backup MX gets and was surprised to see a lot of mail coming through it. Surprised because my primary server is (almost) always available. Upon a closer inspection I was astounded by what I found: all the email that came through the backup MX was spam for the past year was spam. No exceptions!

        Certainly, mine is an extreme case, but I think the trend is very clear.

  • Won't work. (Score:5, Insightful)

    by schon ( 31600 ) on Monday January 22, 2007 @11:19PM (#17719184)
    Most spam bots already send to the *lowest* priority MX (ie. the highest number), and work their way backwards, because it's common for the backup MX'es to have lower anti-spam rules.

    However, this idea would have been *great* six years ago. Once the developer invents a time machine, he's got the spam problem licked for at least a week!
    • by slamb ( 119285 ) *

      Most spam bots already send to the *lowest* priority MX (ie. the highest number), and work their way backwards, because it's common for the backup MX'es to have lower anti-spam rules.

      Do you have any experimental results to back up your claim? Any actual reason to believe it's true? Because he has results that dispute it. Read the article. In his quick experiment, 47% of confirmed spammers tried the primary only, 36% tried the secondary only, and only 17% tried both. While possible that his sample is skewe

      • Re: (Score:3, Informative)

        by schon ( 31600 )

        Most spam bots already send to the *lowest* priority MX
        he has results that dispute it.
        If he does, he didn't post them to his page.

        If you take a look at his page, he says that he used DNSBL.

        DNSBL host != spam-bot

        Spam-bots are a subset of the hosts that would be listed in a DNSBL.

        Next time, before attacking someone, you might want to work on your reading comprehension skills. You'll look like much less of a fool.
      • by wytcld ( 179112 )
        I wonder what our variability is as spam targets. I've seen spam drop markedly with greylisting just on the primary MX. But I can't give a good statistic because I implemented another change at the same time. I'd always set domains up with a catchall that sends unspecified userids to a mailbox, and it's gotten to where for domains that have been around for some years most of the spam coming in is addressed to fake addresses that have been created evidently by other spam faking being from the domain, and the
  • by LibertineR ( 591918 ) on Monday January 22, 2007 @11:23PM (#17719230)
    How many solutions do we have to implement before Spam is outlawed? Why is this shit allowed to go on, stealing bandwidth and all?

    There is more spam than penises needing enlargement, dammit!

    I cant believe this is allowed to go on. How long did it take for callerID and no-call lists to get here? How long before we start putting these people in jail!

    No more bandaids, lock these fuckers up!

    • Because enforcing laws against spam are like enforcing laws against oral sex. How exactly do you plan to track down and punish lawbreakers without big brother style surveillance?
      • by alister ( 60389 )

        Because enforcing laws against spam are like enforcing laws against oral sex. How exactly do you plan to track down and punish lawbreakers without big brother style surveillance?

        A lot of spam is aimed at getting money. So, follow the money (hey, that sounds like a good catchphrase).

    • by Anonymous Coward
      Like it or not, these spammers run extremely profitable businesses. You may not realize it, but they can only continue doing what they're doing because enough people actually do happen to buy the products that they advertise via spam. If people stopped buying items advertised in that way, then the spammers would have no market to sell to, they wouldn't make money, and thus would have virtually no reason to send out spam.

      A number of recent studies have shown that most of the major purchasers of goods adverti
  • by mcrbids ( 148650 ) on Monday January 22, 2007 @11:24PM (#17719232) Journal
    For some time a few years ago, spammers used to IGNORE the primary MX and send to secondary MXs preferentially.

    Since in our case, the 2ndary MX was a dumb sendmail relay only without knowledge of the user DB, it shot the traffic load out thru the roof with bounces to junk spam that, because they couldn't be rejected during the actual delivery attempt, hammered our backup relay.

    This is just a dumb idea.
    • I observed this exact behavior. The reason this was done was exactly as you mentioned - many lowest priority MXs are simply for store and forwarding backup and have no knowledge of the user database. This means the spammer can slam the server without getting rejections. That way the bounces go to the foraged address and the spam server's connection can close faster.
  • by straponego ( 521991 ) on Monday January 22, 2007 @11:25PM (#17719244)
    ...on the assumption that it will be less well-protected than the primary. If many people pull this fake-primary trick, I would assume they'll react quite quickly. This doesn't seem like much of a long-term defense. It looks to me like good defenses will (and do) involve either complex, evolving techniques (think of the p2p/reputation type stuff in razor/pyzor and FuzzyOCR), or hard choices (reject image-heavy messages, whitelist/greylist, etc). No defense, of course, will be perfect.

    Based on watching a few corporate spam sites and even stuff which reaches my private, never-posted addresses, *much* of the spam could be eliminated by moving non-Windows clients. I'm not just talking about zombies. Some of the spam I see hits lists of addresses which are valid and include very difficult to guess addresses inside the company. Once somebody inside your company, or a buddy of yours is rooted, your previously private address is out there; I've never had this happen via any route but a Windows user. Of course, people who CC: everybody they know with idiotic crap instead of BCC: make this problem much worse.

    Oh, and please stop with the lame form letter responses to these articles. It was cute once, long ago. I know at least five people will have posted them by now. Damn spammers.

  • Now the spammers just pushed out an update to their botnets... "Soldiers - try the high MX first."

    Okay everyone, switch your primary back - and don't post it on /.

    Oh, wait... doh!

  • buh (Score:3, Funny)

    by bitspotter ( 455598 ) on Monday January 22, 2007 @11:40PM (#17719366) Journal
    Set the primary MX to . That should keep those buggers busy for a few days. Have fun with those feedback loops, sucka!

    Of course, the same might be true of legitimate senders, as well.... ;p
  • by straponego ( 521991 ) on Monday January 22, 2007 @11:43PM (#17719382)
    Gmail's filtering is, well, badass. I'd think a large number of companies would be willing to pay them to handle email for their domains and forward to a company mail server which only accepts messages via gmail. You'd get a very nice web interface, but could still have the speed and power of a local POP/IMAP server. And virtually no spam. That would be worth a few bucks a month per account for a lot of people. Me, I'd be a little creeped out by them having that much access to my personal emails. Which is why I only use gmail for stuff that I don't want lost in a spam filter, like job searching, financial transactions, attorneys, my friends traveling in the Middle East, etc. But nothing personal!
    • I'm not sure what you mean by "badass." My GMail address fares no better than my Hotmail address. If anything, my GMail address (which I have given only to a few friends and potential employers) gets slightly more spam in the Inbox (although less overall). Maybe GMail is just a bigger target because of how highly it (initially) touted its spam-fighting capabilities, but I haven't noticed a significant improvement.

      I will say that GMail is less likely to mark a valid e-mail as spam though, from what I've n
  • Very strange. I've found that spammers try the secondary MX first, hoping that it has lower filtering than the primary. The higher the MX priority, the higher the probability that it will be the FIRST to be hit. That's why my secondary MX records point to the strictest server in our "cluster"... For a while, it pointed to one that refused ALL mail!
  • by bigberk ( 547360 ) <> on Monday January 22, 2007 @11:55PM (#17719486)
    This probably works in many cases, but as a mail system admin I can tell you that it can fail and will cause problems for legitimate mail delivery. Over the past few months I remember seeing a few messages stuck in my Postfix mail queue, that didn't ever seem to make it out to the recipient's MX. These were domains with deliberately non-functioning MX, and I could not figure out why Postfix was not trying the other MX even though it was up and running. In one case I also tried mailing the recipient domain through gmail, which ALSO failed after many days of retrying. Again I am not sure why the scheme failed to work, but it did fail through both Postfix and gmail which are two very legitimate mail servers.
  • by IGnatius T Foobar ( 4328 ) on Monday January 22, 2007 @11:58PM (#17719504) Homepage Journal
    Sorry, this isn't going to work. It won't even help a little bit. As a long-time email administrator and the author of an email server I can tell you, with absolute certainty, that spammers ignore the priority of your MX records. In fact, they exploit multiple MX's much of the time, by sending spam to your secondary server(s) even if the primary one is up. In addition to extra target capacity, they often manage to take advantage of badly configured secondaries that might not have spam filtering that's as good as the primary, and in many cases the primary has its secondaries whitelisted to make sure no mail gets accidentally dropped.
    • Re: (Score:3, Informative)

      I think this article has it backwards. Spammers often times will go after your secondary MX records instead of your primary. This strategy = waste of time.
  • by Anonymous Coward on Monday January 22, 2007 @11:59PM (#17719510)
    How comes everyone tries to fight spam by breaking infrastructure? Wikipedia neuters links, email server admins delay mails (graylisting) or even reject connections (unlisting), users turn off Flash and Javascript to avoid ads. IMHO, if we have to break our own toys to keep the spammers from playing with them, we're heading for dull times.
    • Re: (Score:3, Insightful)

      by robogun ( 466062 )
      This is the Tragedy of the commons [], a result of selfish use of a common resource by selfish individuals. It's not just spammers and marketers: If my server is getting pounded I might have to take an arguably selfish action by withdrawing it.

      I like to think there's an answer out there in game theory, but with the players numbering in the hundreds of millions if not billions, may be unsolvable.
    • Re: (Score:3, Interesting)

      by Technician ( 215283 )
      How comes everyone tries to fight spam by breaking infrastructure?

      Because spam has broken the infrastructure. A working broken solution is better than a fully broken solution.

      I now use my work e-mail and nothing else. Mail from outside lands in the junk folder as low priority stuff to be sifted later.

      My home private e-mail hasn't been checked since October. It's been hammered to the point of being useless. I've gone to reach me by pager, phone, or business radio.

      I no longer spend 20 minutes a day sortin
  • They will respond (Score:4, Interesting)

    by btempleton ( 149110 ) on Tuesday January 23, 2007 @12:01AM (#17719532) Homepage
    But they're often slow to respond. Hell, I changed a DNS record when I moved servers once and spammers will still going after the other server, with no DNS record pointing to it, for 6 months because they use static caches.

    Many people were already using this trick, probably hoping it wouldn't show up as lead story on slashdot.

    In some ways, selfish ways, it's like the story of the two hikers who face a bear. The first hiker immediately sits down and starts putting on his running shoes. The other says, "What are you doing? You can't outrun the bear!" The first hiker says, "I don't have to outrun the bear. I just have to outrun you."

    Many spammers, faced with a failed attempt at sending mail, do not bother to retry or try other MX. Instead, they just move on to the next target in the list, since trying a new target is just as easy as retrying an old target. No real difference to them. But it means you just push your spam attempts onto other people who haven't elected to bend the standards to divert the spammers.

    The "good" spam sending programs run many threads, timeouts don't punish them, their limit is more the bandwidth. Attempts to divert spammers onto others who have not tried the tricks should create an ethical question. Are we just arranging for the bear to eat our friend?
  • by arthurpaliden ( 939626 ) on Tuesday January 23, 2007 @12:13AM (#17719632)
    ISPs must restrict clients to 'n' emails (ie free minutes) per day based on their type of account. If they want to send more they have to pay.
  • Just like MailHurdle (Score:2, Informative)

    by jonnythan ( 79727 )
    It sounds like a function called MailHurdle that's built into Mirapoint email filters.

    It works wonderfully. We've been using for about a year at my organization. It works by initially rejecting all incoming mail from unknown servers. If the server is legit, it will retry the email, and on that retry, MailHurdle will allow the mail through.

    It instantly eliminated well over half of our incoming spam. Very clever technique, and it certainly works.
  • by dtdns ( 559328 ) on Tuesday January 23, 2007 @01:41AM (#17720192) Homepage
    I was reading the article, and suddenly port knocking came to mind. It wouldn't be a far stretch to modify an SMTP server to only reject connections on the lower priority IP address if the source had not tried to first connect to the higher priority IP address.

    Instead of blocking the connection to the primary at a firewall or using an "unused" IP address, the primary SMTP server could give a greeting banner and then immediately return a "temporarily unavailable" status code (and cache who was connecting there).

    In other words, an RFC compliant MTA should be connecting to the higher priority host as defined by DNS first, then fail over to the lower priorty host, in order. If an MTA tried to connect directly to the secondary MX first it could be rejected with a temporary failure status code which a spammer is likely to ignore. It would require the SMTP receiver to keep a cache of who had connected to what IP addresses within a certain time period which would eat up some memory depending on traffic load. We already cache reverse DNS lookups and RBL lookups, so it could probably be done.

    With this setup you would have two MX records for your primary mail server that your SMTP server would be active and listen on. It would just track the order of connections to ensure that the remote MTA was following the rules before it allowed the source to get past the greeting banner.
  • I for one... (Score:4, Insightful)

    by deblau ( 68023 ) <> on Tuesday January 23, 2007 @01:49AM (#17720236) Journal
    I for one welcome our soon-to-be-RFC-compliant spammer overlords. I mean, we want standards compliance, right? Right??
  • by mosch ( 204 ) on Tuesday January 23, 2007 @02:29AM (#17720404) Homepage
    I have read some truly terrible ideas on this website. (Usually followed by a chorus of inexperienced idiots blindly saying how great they are, while all the skilled and experienced people rolled their eyes.)

    This is one of the worst ideas I have ever read. Intentionally introducing a large and unpredictable delay into the receipt of all e-mail.

    What's next, a recommendation to cut down on telemarketing by setting your PBX to automatically disconnect 50% of all incoming calls?
  • This doesn't work (Score:3, Interesting)

    by macdaddy ( 38372 ) on Tuesday January 23, 2007 @09:52AM (#17722720) Homepage Journal
    I can't believe someone that claims to have anti-spam knowledge is suggesting this when in fact the opposite is true. Spammers frequently forgo opening an SMTP connection to the MX with the highest priority (lowest numeric value) and instead opt for the ones with the lowest priority. They do this hoping that the secondary MX doesn't have the same spam-fighting abilities as the primary MX. They're hoping that it's a simple backup or that it only queues for the recipient domain in question and doesn't validate recipient userids. The spammers hope that the primary MX will accept all mail blindly from the secondary, as is usually the case. This has been a long-standing theory that hasn't ever been disproven. This jives with what I've always seen on all my MXs.
    • Re: (Score:3, Interesting)

      That's what I thought, too. But then I thought, 'make your highest AND your lowest priority servers dummies.'

      • Re: (Score:3, Interesting)

        by macdaddy ( 38372 )
        LOL. I heard that suggested once. I haven't tried that one. It can't hurt to try it. My favorite method is SMTP tarpitting. That's always fun.
  • I WTFA... (Score:3, Informative)

    by jumperboy ( 1054800 ) on Tuesday January 23, 2007 @11:43AM (#17724016)

    ...and encourage readers to RTFA, where I've addressed many of the issues brought up in these comments. I also encourage people to try the technique, if they are in the position to do so (admins only, this is not a solution for endusers), and evaluate it for themselves. Or not. It's true that most new antispam solutions are dreamed up by crackpots. I might be a crackpot. If this possibility concerns you, don't be an early adopter. Wait and see.

    It's true, in my experience, that Nolisting stops some spam with no false positives (in my experience). And that's a Good Thing. But it doesn't stop significantly more spam than a combination of other techniques, which I also implement. Some of those techniques use a lot of resources, such as content filters (often powered by perl) and virus scanners. Nolisting provides a way to free up some of those resources, possibly resulting in better performance and even hardware savings. These savings can be significant at large sites that currently scan each and every message that arrives.

    Nolisting can be bypassed. I don't make any wild claims. Spammers can get past it easily by going directly to the secondary MX. Guess what? They already do that, and have been doing that well before greylisting was introduced. Nolisting significantly reduces the percentage of spam my MX processes, thereby freeing up resources. It's just one part of a layered solution.

    I've limited secondary MX access by extending Nolisting into Unlisting (Port Knocking for SMTP): []. It's wildly effective, except for one serious problem: A retry might originate from a different IP. This appears to be legal, and seems to be the result of load balancing strategies adopted by some important sites. For that reason I don't recommend it. It will randomly block messages from gmail, for example. You can't reasonably predict the IP a multihomed host will use for a retry, so be very skeptical of any approach that claims to have solved this problem.

    Unwanted email is annoying. When it carries a payload, it is potentially dangerous. But I don't really view this as a security issue. I don't buy the argument that Nolisting is security by obscurity, and therefore bad. It's a form of access control, a gatekeeper, a prophylactic. It's an apple a day, not a cure for cancer. It's not addicting, fattening, or life-threatening. Try it, if you're looking for ways to improve the health of your mail system. Discontinue use immediately at the first sign of complications. Side effects include more sleep and time spent with your kids.

    Nolisting rarely introduces delays. As I point out in the article, most relays retry immediately. Any relay that cannot get beyond Nolisting is seriously, seriously noncompliant. While I don't suggest Nolisting as a complete replacement for Greylisting, it is a viable alternative for sites that experience problems with Greylisting and find the delays it introduces to be unacceptable. As the name implies, Nolisting is meant to used without dependence on whitelists. Wider adoption and testing will determine if this ideal has been realized.

    Like Greylisting, Nolisting breaks infrastructure to some degree. Many admins find this distasteful. I know I do. If Nolisting becomes widely adopted, logs will become fatter with "Connection refused" errors when the primary MX doesn't respond. I'm sorry for that. But our logs are already fat with 45x errors from Greylisting, RBL disconnections, SpamAssassin scores, etc. Nolisting might even help to make logs smaller, if you currently see a lot of these messages. Time will tell. Keep an open mind, and remember that we often make concessions to improve a system's overall health. Just reducing the possibility of another zombie being created on the Internet creates benefits for everyone.

    Try it before you draw a c

  • SPF... (Score:3, Insightful)

    by msimm ( 580077 ) on Tuesday January 23, 2007 @02:01PM (#17725934) Homepage
    For now I'll stick with SPF [] and old fashioned spamassassin (milter).

    And whats with the anti SPF sentiment? Its not like we've got a lot of more effective alternatives on the market and the only real argument I read is the rejection of real email, when softfail pretty much takes care of that (then leaving it to spamassassin to decide if the mail is legit).

    We send an receive a good deal of email and I certainly wish SPF was more common. I'm tired of forged bounces and the *slew* of undeliverable responses 'dumb' servers return to our system every day.

    Yet instead of taking any real action we bicker while spammers laugh all the way to the bank. Their is no magic bullet, but from my POV SPF is the closest thing yet (unless my DNS gets hi-jacked, but then I'm fucked anyway).

Where it is a duty to worship the sun it is pretty sure to be a crime to examine the laws of heat. -- Christopher Morley