Slashdot Mirror

← Back to Stories (view on slashdot.org)

Spam Blocking Engine for OpenBSD

Posted by michael on from the two-scoops-white-rice dept.

mkeke writes "In a post over at OpenBSD Journal, Theo states that he has written a spam blocker that works with pf and Spews. It looks darn cool :)"

24 of 278 comments (clear)

  1. 550? 450? by Habbie · · Score: 5, Informative

    I assume he means a 450 reply, not a 550? 550 won't make the message stay in the queue, 450 will.

    1. Re:550? 450? by edgarde · · Score: 5, Informative
      450 says there's still a mailbox there. 550 says not found. Here's a list of SMTP codes.

      Incidentally, the code actually has a command line option to choose between 450 and 550.

  2. Spews = /m\ by joeszilagyi · · Score: 5, Insightful

    Why even bother with Spews? Why not Spamcop, who doesn't block half the planet?

    --
    Dude, where's my packet?
    1. Re:Spews = /m\ by PacketMaster · · Score: 4, Interesting
      And spews doesn't? Spews randomly blocked a consulting company's netblock I worked for part-time simply because that our block was next to a "known spammer's" block. When they politely asked to be removed and pointed out that according to their own evidence file that their netblock had nothing to with spam, they were met with very hostile responses and told to essentially ditch their teleco provider because they'd never unlist anyone. They admitted that they simply block IPs in a form of "collateral damage" because they feel like it to hurt legitimate businesses so they flee their network provider. Look at antispews.org for more info on their flagrant abuses and why you shouldn't use spews.

      ... generally doesn't cause innocent third parties distress while attempting to achieve his goals.

      Using spews is going to cause third-party distress.

      --

      Some people take their .sig way too seriously

    2. Re:Spews = /m\ by Just+Some+Guy · · Score: 5, Insightful
      Your company was paying that ISP. Thus it was also supporting spam.

      I understand the principle involved, and admit a fair bit of sympathy for that point of view. However, for some of us, switching ISPs isn't a luxury we have. I live in a small Midwest town. My options are:

      • DSL/wireless via the local dominant ISP
      • DSL via MSN
      • Cable modem
      • Dialup via one of those "unlimited access for only $6.95!!!!" companies
      Out of that list, the first option is the only one viable for hosting servers, since the rest either block service ports, have onerous TOS contracts, or just aren't serious connections.

      Say that I discover that the local ISP (which has probably a 98% market share here) has some customers with open relays. What do I do? Buy a T1 and contract with Qwest, or get out of online business altogether?

      In practicality, I don't have the option to switch, regardless of my ISPs policies.

      Fortunately, the provider is run by a great set of people, and employees several real system administrators, so I don't really have to worry about this hypothetical problem. That's a Good Thing, because I'm pretty well stuck where I am.

      --
      Dewey, what part of this looks like authorities should be involved?
  3. Re:difference by fruey · · Score: 4, Interesting
    SpamAssassin uses keywords, RBL listings, et al.

    This is just a lightweight SMTP server which takes over anyone who is SPEWS listed and rejects them. A decent server like Postfix + amavisd & SpamAssassin will already do this with little overhead.

    More reinvention of the wheel, I fear.

    --
    Conversion Rate Optimisation French / English consultant
  4. Re:difference by bconway · · Score: 5, Informative

    SpamAssassin is nothing more than an advanced filter. This stops the spam before it gets to you and fills up the offending mail servers disk space with it.

    --
    Interested in open source engine management for your Subaru?
  5. Re:difference by Zigg · · Score: 4, Informative

    Err, SpamAssassin isn't exactly what I'd call "low overhead". While it's pretty good at what it does, it still has potential to slow my 32MB mail server to a crawl unless I tell spamd to process only one message at a time.

    And that's only filtering my mail.

  6. Spews is NOT the right way to filter e-mail. by Sturm · · Score: 5, Informative

    Spews is EVIL. Plain and simple. They block IPs based soley on the fact your upstream provider hosts or has hosted in the past, someone the SPEWS "admins" (and I use that term losely) believe to be spammers. It is impossible to get off their list and if you are a customer of C&W you probably have IP space being blacklisted by them. Blocking large blocks of class Cs, just because someone happens to share IP space with an alleged spammer is the WRONG way to filter spam.
    Please take a look at http://www.antispews.org for more information before using SPEWS.

    1. Re:Spews is NOT the right way to filter e-mail. by jamie · · Score: 5, Interesting
      "Spews is EVIL... Please take a look at http://www.antispews.org"

      Thanks for the link. I'll confirm that Spews is not the way to go. Well, it depends on whether your goal is to block spam for your users, or just to piss people off.

      If you're a network admin and you want to block spam for your users, try something else.

      If you just want to piss people off, Spews is great. My personal mail server (very kindly hosted for me for free on a friend's network) was put on Spews' blacklist. My server has never in its lifetime sent a single spam, of course. But Spews had found four (count 'em) examples of spammer websites (not spam-sending machines) on the IP blocks owned by the people who my friend bought access from, twice removed. Because of these four claimed spam websites, Spews put FOUR CLASS A's on their list.

      That's right -- a quarter-million IP numbers were blocked because they didn't like the policies at four IP numbers.

      Wait, did I say four? When I checked up on them, two had already moved to other providers, one I couldn't find, and only one was still there. So my server, and a quarter-million others, were being blocked because the Spews people disagreed with one solitary website. Hosted by a company that I have no relationship with.

      It goes without saying that attempts to get my server whitelisted failed.

      And I do question the value of their blocking my mail server. Like I said, I was being hosted for free just because I have helpful friends... my moving to another network actually saved them money!

      Somehow, I think most net administrators, if they knew that Spews' purpose was political and not technological, would be less likely to use it. There are plenty of other blacklists out there. What are the good ones that don't hijack your networks to apply political pressure?

  7. big difference: not just rejecting mail by agshekeloh · · Score: 5, Informative

    It doesn't reject messages. It defers them forever, telling the open relay to "try again later."

    This tool is a weapon against open relays. The goal is to fill up the open relay's hard drives by deferring the incoming mail, rather than just rejecting the messages.

    Yes, you can do this with other blacklists as well, but nobody seems to be actually doing that.

  8. It thougt it was spam though by neurostar · · Score: 5, Funny

    ...doesn't block half the planet?

    I thought half the email on the planet was spam though!

    :)

  9. SPEWS is necessary & effective at hurting spam by Charles+Dodgeson · · Score: 5, Insightful
    Time and again we see case after case of some provider that
    1. Let some customers spam
    2. ignored abuse complaints
    3. did nothing while when that particular spammer's IP was listed.
    4. Only took action against a spammer when the SPEWS listing expanded to include non-spamming customers
    5. Whinged that SPEWS was unfair and not the right way to do things
    Every day SPEWS proves itself necessary and effective at getting otherwise unwilling providers to remove their spammers. Note that SPEWS uses an escalation process. The provider has to ignore complaints for a while to have the IP range expanded to include non-spammers

    If you can suggest something that is half as effective at raising the cost for spammers as SPEWS, please suggest it. SPEWS forces providers to decide whether they want to host exclusively spammers or host exclusively non-spammers.

    But if your goal is merely to filter spam (making life easier for the spammers) then you are right. SPEWS is not the way to do that.

    --
    Prime numbers are exactly what Alan Greenspan says they are -S. Minsky
  10. Re:difference by grub · · Score: 5, Interesting


    Can anyone explain why you wouldn't just use SpamAssassin?

    Once the spam is in your system then your bandwidth, disk space and other resources have already been consumed by the spammer. This prevents the spam from ever coming into your network and put the burden of the load back on the spammer's shoulders.

    Damn fine work.

    --
    Trolling is a art,
  11. Re:Platform [In]dependence by evilviper · · Score: 4, Informative

    Are you not familiar with the concept of open source? Instead of saying "Gimme Gimme Gimme" you could do it yourself, or even contract someone to do it. If you aren't going to contribute, don't start complaining that others should be contributing more.

    --
    Slashdot gets worse every day... Pipedot: News for nerds, without the corporate slant
  12. I'm Disappointed by TerryAtWork · · Score: 4, Insightful

    I remember when I applied for a Mead mailing list and got a nasty letter back saying 'your SPAM has been rejected!' just because I sent it from a Rogers.com address, so I know what it's like to be blacklisted like in SPEWS, and it sucks. That's not the way to do it.

    Also, this new spam program retaliates and the law is very nasty about vigilantism and retaliation, perhaps because it threatens their monopoly. I don't want to see a spammer WIN in court, do you?

    Also, program like popfile doe a great job of removing spam.

    My advice is to forget kicking the spammers ass and just make their work vanish down a black hole like it will WHEN BAYESIAN TECHNIQUES ARE USED AT THE ISP END hint hint...

    --
    It's Christmas everyday with BitTorrent.
  13. Use a Teergrube by Brett+Glass · · Score: 4, Informative

    What Theo should be doing, instead of sending a 5xx response (which, by the way, won't keep the message in the spammer's queue; a 5xx is a final rejection) is to redirect spammers' connections to a Teergrube (a spam "tarpit"). If enough people do this, the spammer will be slowed down greatly.

  14. Re:SPEWS is necessary & effective at hurting s by jamie · · Score: 5, Insightful
    "If you can suggest something that is half as effective at raising the cost for spammers as SPEWS, please suggest it. SPEWS forces providers to decide whether they want to host exclusively spammers or host exclusively non-spammers."

    First of all, I don't think most network administrators -- or their bosses -- know what they're getting into when they use Spews to police their network. If you are an admin who signs your company up for it, be prepared to have this conversation:

    Boss: Hey, can you check to see if there's some kind of network trouble. I haven't gotten a reply email from a client in three days.

    You: (after checking) Ah, that mail server is spam-friendly, we reject their mail.

    Boss: (confused) They're not a spammer, they're our best client.

    You: No, but they buy bandwidth from someone who buys bandwidth from someone who...

    Boss: What?

    You: We're using SPEWS, which is the most effective tool at stopping spam around the world! It forces providers to decide whether...

    Boss: I don't give a damn, you work for me, not people around the world. Your job is to make the email work, not be a do-gooder. You may have cost this company a contract. Now get the damn mail working and tell me how many times you bounced my client's mail so I can decide whether you still have a job.

    And -- you think Spews is effective? After being put on their list I had a grand total of one person unable to receive my mail. I have a dozen other people using my server to send and receive mail to hundreds of people, and according to my logs, among all of us, the sum total of people who couldn't get our email was two. That's the most pitiful boycott I've ever seen.

  15. rblsmtpd + spamassassin by Gothmolly · · Score: 4, Interesting

    Works great for me, thank you DJB! Here's a summary of the spamhouses I've blocked (with a 553 error code) over the past few hours. These never even touch spamassassin.

    64.70.22.99-outbound1.lamailer.com
    209.236.32.1 57-
    216.19.164.127-127.opti9.com
    65.126.119.178- formulatedmail.com
    64.201.128.3-netblock-64-201-1 28-3.stanfordintl.co m
    66.216.111.187-mail213.rm23.com
    63.96.237.154-
    216.109.73.35-om40.yourmailsoure.com
    211.90.191 .61-
    204.73.107.103-
    209.189.49.102-
    209.123.11 1.22-mail.dmx4.com
    216.19.163.204-204.sbase30.com
    63.70.105.139-ntls1.digitalriver.com
    66.197.162 .15-
    209.47.251.15-smtp5.rapid-e.net
    209.236.57. 176-mtsbp512.email-deliveries.net
    202.103.64.43-
    66.216.116.78-mail153.myfunsleuth.com
    65.107.195 .162-
    209.213.210.18-mailer18.labeldaily.com
    200 .206.207.206-200-206-207-206.terra.com.br
    66.216. 115.56-mail16.justforyou-mail.com
    64.119.213.95-p assionup.com
    66.216.107.233-mail233.dealdelivery. com

    --
    I want to delete my account but Slashdot doesn't allow it.
  16. Interesting, but here's an extra twist by wowbagger · · Score: 5, Interesting

    I won't go into the validitiy of using SPEWS as a blocklist - there are good arguments pro and con there.

    But here's a twist to the basic idea:

    Given the the email sender is in $BLOCKLIST, have the filter daemon give the 450 response

    v... e... r... y... ... s... l... o... w... l... y...

    Combine a teergrube with the 450 response to fill up both their mail spool AND their socket connection table.

    (For those who don't know, a teergrube (tarbaby) is a mail server that response slowly to a spammer, the better to tie up his connections).

    Now, not only will the open relay's mail queue fill, but it will run out of (file descriptors|sockets) and choke on that too!

    --
    www.eFax.com are spammers
  17. Re:Good concept - quality of execution pending by Dunark · · Score: 4, Insightful

    I don't see the hypocrisy. If a neighbor of mine allows people to cross his property so they can dump garbage on my property, where do I get the obligation to accept the garbage? What's wrong with me putting up a fence and letting the garbage pile up on his side?

    If someone wishes to run an open relay and be a conduit for spam, why should he be granted immunity from consequences?

  18. Re:SPEWS is necessary & effective at hurting s by binner1 · · Score: 5, Interesting

    At my last job, that is exactly the conversation I had. My boss said: We get too much spam here, do whatever it takes to stop it. I said: Sure, I'll have qmail do some rbl polling before accepting mail. Worked great for about a month...cut roughly 50% of the spam that network received. Then, boss says: Why can't I get email from ebay seller X? I say: Oh he's rbl'd...we don't take mail from there. He says: Ok, turn off the rbl.

    After that, I turned on my own bayesian filtering and said F the rest of the network/users.

    -Ben

  19. Re:Back Off by almeida · · Score: 4, Interesting

    I don't see how it's wrong to send it back to the open relay. They are saying, "Here, have this," and you are just replying, "Not right now, thanks." That's perfectly valid use of SMTP codes. It's not like you launch an attack every time you get email from these relays, you're just telling them you don't want it right now. The idea is just to take the pain of SPAM away from the user and give it to the ones responsible (to some extent) for it. The open relays caused it, they should deal with it.

  20. Antispews is spam; SPEWS is good; others are too. by Frater+219 · · Score: 4, Informative
    Please take a look at http://www.antispews.org for more information before using SPEWS.

    Actually, antispews.org is likely being operated by spammers, as the Osirusoft FAQ suggests. (If nothing else, they are spammers of USENET newsgroups, since they kiboze for references to "SPEWS" and troll in response, much as Serdar Argic once did with "Turkey".) Naturally, spammers are pissed off at SPEWS, because it is simply put the most effective tool presently in the field for denying spammers access to (1) victims, and (2) willing ISPs to host them. Innumerable spammers have been terminated as a result of SPEWS listings.

    There is no conceivable informed controversy as to whether or not SPEWS is effective at getting spammers off the Net. Whether or not SPEWS is a good tool for your site to use as a tool for reducing your spam count is quite another question. In my personal experience (as a security and email administrator for my site, which is a research institution) SPEWS is extremely valuable. I read my mail logs and ascertain that SPEWS usage blocks spam, with a remarkably low incidence of false positives.

    In the past week, our incoming mail server has blocked 969 messages on account of SPEWS, with zero reports of false positives from our users. (To be honest, we get about one such report a month, and we whitelist the offending IP address. It's usually in China; we have several Chinese researchers.) Our locally maintained blacklist blocks about twice as much spam, and our use of sbl.spamhaus.org blocks about five times as much -- but that is biased by the fact that we consult those lists before SPEWS, and there is a good deal of overlap between them.

    I would not recommend that ISPs who offer email service to their users use SPEWS by default, though it would be a valuable optional service. The DNSBLs I would recommend everyone use are:

    • sbl.spamhaus.org, which lists only netblocks occupied by known repeat spam offenders
    • relays.ordb.org, which lists only open mail relays; and
    • proxies.relays.monkeys.com, which lists only open proxies.

    These are all low-to-no-false-positives lists which I feel comfortable recommending to every ISP regardless of its stance on SPEWS.