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Do spam filters read Alt-Text?

April 9th, 2009 | by Ben

firefoxscreensnapz008Someone over in the MailChimp Jungle asked, “Do spam filters read Alt-text descriptions?” I honestly had no idea, so I took my most recent MonkeyWrench email newsletter, replicated it, and I typed in the most awful, disgusting alt-text descriptions that I could think of.

Seriously, I had to wash my fingers after typing such nasty stuff, and I couldn’t look at myself in the mirror for a day or two.

In addition to the yuckiness, I typed in a bunch of stuff about gambling, and some phishing type content. And I made sure to use all caps, with lots of exclamation points (see why spam filters hate that).

Then I ran it through our Inbox Inspector’s Spam Checker tool…

Turns out I passed all the major spam filters!

My Spam Assassin score wasn’t great (anything over a 5 is DOA but I like to stay well below 3). But that seems to be because of other problems.

In terms of the extremely disgusting alt-text descriptions I used, they don’t seem to have triggered anything at all:

spam-filter-check

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Posted in Ask MailChimp, Copywriting, Deliverability, Email Design, MailChimp News, Monkeys!, Spam Topics, Tips, Tricks, Best Practices, Using MailChimp | 8 Comments »

8 Comments

    • Dave Savatski says:

      That is one sweet video! Oh Mail Chimp, I heart you. I’ve thoroughly enjoyed learning to use Mail Chimp and wow fellow employees with my recently acquired knowledge of spam filters and ninja skills provided by Mail Chimp. Keep up the good work!

      Reply to this comment
    • J.D. says:

      Spam filters almost always look at the entire message as raw text, rather than as a rendered HTML page — so the alt text will be treated the same as any other text.

      I think what your test actually showed was that those particular bad words aren’t, by themselves, sufficient triggers for spam filters. That makes sense, since most of ‘em stopped doing raw keyword filtering long ago and moved towards other methods.

      Humans, however, still read those words when they decide whether to open a message or report it as spam — so a campaign offering “FREE HOT WET VIAGRA!!!!!” will end up with poor delivery.

      Reply to this comment
    • Ryan says:

      Actually, it looks like SpamAssassin might have picked up on at least one thing in your ALT text. See the line “BODY: IMPERATIVOS/EXCLAMACIONES EN MAYUSCULAS”?

      I have no idea why that’s in Spanish, but it means “Commands/exclamations in all caps”

      That’s 35% of your not-so-great SpamAssassin score.

      Reply to this comment
      • Ben says:

        Hey, you’re right. It picked up the exclamation points, but not the words I used before it? That is odd.

        Reply to this comment
    • Paul says:

      The inbox inspector’s ‘content assessment’ tab will show “spammy words” and those words can come from alt-text I believe.

      Reply to this comment
    • Doug says:

      I must say, without coming across to arrogantly Ben, that i am surprised that this question recieved the answer it did from you.

      My understanding of email filters and spam engines (some of this is from actually reading some of the OS engines’ codebase) has always been that they simply read the HTML in the email as flat text.

      This would lead me to strongly agree with JD’s post above.

      From a technical view point your post seems quite unsavvy in both its original question and its tested result.

      Sorry to say the above as i love the service to death. It just worried me that such a technically minded company would post such a non-technical experiment – it leads us to believe you are not the oober dojo ninja’s we once thought you were. And thats bad – as chimp ninja’s are cool…

      Reply to this comment
      • Ben says:

        hi Doug, that’s not arrogant at all. I’m the first to admit I have no idea what I’m doing. I just draw monkeys. :-)

        However, I do think this was a good, semi-scientific test. Maybe it was just a bad blog title. The actual question from our customer was, “do spam filters penalize me for bad alt-text?” Which is a good question.

        Instead of just telling them the seemingly obvious answer (”you should assume that spam filters will just read everything as flat text”), I decided to run an experiment.

        I took my own campaign that scored very well (good content, healthy mix of text + images), and added the most disgustingly bad alt-text descriptions to several images. I used words and concepts that gave very high spam scores found at:

        http://spamassassin.apache.org/tests_3_0_x.html

        Then, I passed it through our inbox inspector, which scanned it in Spam Assassin, Postini, Barracuda, Cloudmark, MessageLabs, and other major spam filters. Not one of them (except, as one user pointed out, the one with the espanol criteria) called me out on my alt-text content, and my score was still _technically_ a passing score.

        Doesn’t mean I’m right and you and J.D. are wrong. Or vice versa. Maybe spam filters read alt-text, but then ignore it. Maybe they’ve learned that alt-text is usually ignored by lazy spammers, so the mere presence of alt-text is a good thing to them (even if the content’s bad). Maybe they ignore anything inside an IMG tag. Maybe the inbox inspector was off that day. But if you CTRL+F around that spamassassin criteria page above, there’s no mention of alt-text that I can find (not that the list there is all inclusive).

        FTR, my point isn’t that senders can go nuts with alt-text. It just means that as I’m coding my HTML emails, alt-text is one less place I have to worry about triggering something by accident. So, when I paste a photo of my programmers having a water-gun fight in the office, I don’t have to pull out a thesaurus to come up with alternatives for “hardcore nerds having wet fun around the office.” It’s a decent alt-text description that might actually convince recipients to turn images on.

        Maybe I can do some more testing. Like removing the alt-text completely, to see if leaving it blank hurts my score worse than putting in nasty stuff.

        Thanks for your input, and never hesitate to call me an idiot. :-)
        All conversation is good, right?

        Reply to this comment

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