Fight Spam With Nolisting

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)."

Oblig.

[Whiney Mac Fanboy (963289)]

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.

[um... Lucas (13147)]

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.

[arivanov (12034)]

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.

[AchiIIe (974900)]

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)

That's "greylisting".

[khasim (1285)]

"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.

Re:That's "greylisting".

[by Anonymous Coward]

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 :-(

Re:That's "greylisting".

[Dion (10186)]

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.

Re:That's "greylisting".

[pe1chl (90186)]

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.

Re:That's "greylisting".

[AchiIIe (974900)]

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: http://it.slashdot.org/comments.pl?sid=132222&cid= 11045587 [slashdot.org]

From the FAQ (http://www.olympus.net/doubleVerifyNL):

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.

Re:That's "greylisting".

[RazzleDazzle (442937)]

Remember, the spammers have, effectively, unlimted bandwidth and unlimited processing power at their disposal.

If the big companies started doing this [benzedrine.cx] 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.

Zero Spam is easy...

[Kent Recal (714863)]

I use qconfirm [smarden.org] myself but there's also tmda [tmda.net] 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:Oblig.

[geminidomino (614729)]

If you do business with clients who send $important_financial_information over inherently insecure and unreliable protocols, you have bigger problems than spam.

Re:Oblig.

[shellbeach (610559)]

Fine in principal, not so fine if the non-compliant SMTP sender belongs to a client of yours sending a $important_financial_email.

No kidding - just look at the $important_financial_email from a non-compliant SMTP sender I got in my inbox this morning:

Dear Partner,

My name is Sgt James Clayton. I need your help in keeping the money that we moved from Ba'qubah in Iraq safe. We moved this money some months ago to a Security Company in Italy. You know the funds are legal and it is oil money. we want to move the funds from Italy now to a secure place or location. Can you provide that? The total amount is US$25 Million dollars in cash. This money is in cash and we want to move it to you as soon as possible. Mostly $100 dollar bill notes.Total of US$25 Million dollars. So your share for helping me is US$12.5 Million dollars.Will you help? The whole process is simple and straightforward. I am still in iraq and i will be discharged soon but no one knows when this War will be over. I dont want to take any chances of loosing the funds. That is why we must act now.We are sharing everything 50/50. This is a legitimate transaction. If you are interested, i willprovide you further details and instructions. Please keep this confidential. We can't affo
  rd more political problems. Can i trust you and will you help? Waiting for your urgent and positive response. Please send your full contact details so that i can reply you back asap. If you have any questions please feel free to ask, I look forward to hearing from you.

Yours Truly,

Sgt James Clayton.

Re:Oblig.

[ArsenneLupin (766289)]

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).

Yep Funny

[keeboo (724305)]

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)
No

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!

Address Book

[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.

Re:Address Book

[dgatwood (11270)]

Flowchart:

• 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

Re:Oblig.

[jon787 (512497)]

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:

[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.

Re:Oblig.

[dangitman (862676)]

No. Email spam was unleashed upon the world by Hormel as a marketing strategy. People just weren't thinking about spam anymore - this has gotten the brand name firmly back in the public's mind. It also has huge kitsch appeal now. Especially as kids grow up who only know of email spam, not SPAM the spiced ham. They'll see SPAM at the supermarket - and say "Look! It's spam that's not spam. OMG! Physical spam! LOLzors, I must buy this to replenish energy lost by playing with my Wii!"

We salute you, Hormel marketing, our spam overlords.

Re:MOD PARENT UP +5 THE FUNNAH

[eric76 (679787)]

The first time I ever saw one of those "forms", I thought it was interesting.

The second time, I thought it was "ho-hum".

After hundreds, maybe even thousands, they are just plain lame.

The only good thing about them is that you instantly know that you can skip over them and not miss anything at all.

Temporary Solution

[PhotoGuy (189467)]

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 :)

Re:Temporary Solution

[TheSkyIsPurple (901118)]

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.

Spammers often try secondary MX's.

[khasim (1285)]

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:Temporary Solution

[Frogbert (589961)]

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.

Re:Temporary Solution

[tdelaney (458893)]

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.

Re:

[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:

[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

Short Term Solution

[pyite (140350)]

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.

funny

[User 956 (568564)]

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.

OT - Re:funny

[proverbialcow (177020)]

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.

I run a mailserver, this is a bad idea

[Gothmolly (148874)]

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.

I run a high volume mailserver, this is a bad idea

[chathamhouse (302679)]

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!

Re:I run a high volume mailserver, this is a bad i

[anakog (448790)]

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.

[schon (31600)]

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!

This is bullshit!

[LibertineR (591918)]

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!

Re:

[rblum (211213)]

Yawn. Not that old saw. Spam is not free speech - it's commercial speech, which has always been regulated. Hint: "Free Speech" does not mean that you can say whatever you want, whenever you want.

Re:This is bullshit!

[LibertineR (591918)]

Idiot!

Spam is NOT free speech. You cant come into my home screaming penis ads at me without getting your ass kicked, so why should you be able to do it into my mail server?

Re:This is bullshit!

[corbettw (214229)]

You need not open your mail, esp. when the subject line is something that you aren't interested;

You need not open your mail to have your resources (bandwidth, disk space, processing power) consumed by spam. I work at a major telecom company running the edge mail servers, along with another full time engineer. Of the 12 million emails we get a day, about 100,000 are legitimate mail. The rest is just spam, and it uses up the bandwidth that could've been resold to customers, it uses up the disk space on the expensive mail servers we bought a few months ago, hell it forced us to buy those expensive new servers in the first place. I figure, just in the extra salary (if not for the spam one guy would be enough to handle the load), having to upgrade perfectly adequate five year old servers, and buying licenses for anti-spam products at four different levels of mail delivery throughout the enterprise just to keep our users from being deluged with useless garbage, the company has spent about $200,000 last year, and will spend about the same amount this year. All because a bunch of asshats want to force our employees to read their idiot advertising, using our network resources to push their message.

That's not free speech, that's theft. And that's never been legal.

Attacks on 2ndary relays

[mcrbids (148650)]

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.

Some spammers target secondary MX first

[straponego (521991)]

...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.

buh

[bitspotter (455598)]

Set the primary MX to 127.0.0.1 . 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

And WHY won't google rent out Gmail's filters?

[straponego (521991)]

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!

Not as good an idea as it sounds

[bigberk (547360)]

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.

Spammers IGNORE the MX priority

[IGnatius T Foobar (4328)]

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.

What's with the breakage to fight spam?

[by Anonymous Coward]

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.

They will respond

[btempleton (149110)]

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?

The only solution...

[arthurpaliden (939626)]

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.

Nolisting + Port Knocking?

[dtdns (559328)]

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...

[deblau (68023)]

I for one welcome our soon-to-be-RFC-compliant spammer overlords. I mean, we want standards compliance, right? Right??