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So we did some SPAM tests on the emails we're sending, and SpamAssassin gives the HTML_IMAGE_ONLY_12 label to this email.

The description says This may indicate a message using an image instead of words in order to sidestep text-based filtering.
But the email has no images at all.

It is indeed a bit short, but as it has no images, that shouldn't make it suspicious of being SPAM.

Here's the email's content:

Thank you for your interest in following me.
Please confirm that you would like to receive email updates by clicking the link below.

Yes, I want to follow John Doe

Thank you
John Doe

So what should I do to avoid this?
Just include filler text?

Petruza
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2 Answers2

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Ahh SPAM_ASSASSIN. I have used that for years with success. I understand what you are saying, however SPAM_ASSASSIN is not perfect. Sometimes false readings will popup if triggered. The only way I see this affecting you is that the HTML_IMAGE_ONLY_12 score is making the email marked as SPAM. You can either lower the score, or if there is no affect, ignore it. Also, look at the size of the email. If it is just text, it should be 1-2Kb. If it is larger, then the email author has snuck an image into the email. Hope this helps.

  • The thing is the author is us, and the email is what I quoted above, no images, just that text. – Petruza Oct 26 '16 at 15:43
  • Interesting. Was the email size small? Well, regardless of whether there is an image or not, it seems the issue is the HTML_IMAGE_ONLY_12. I have seen SpamAssasin do false detections, that is why I suggested to change the score. Every once in a while I had to just make the score 0 on certain rules to stop the false detections. hopefully you find a solution that works. –  Nov 11 '16 at 13:35
  • OP/others: as @doug-d mentions - Even though you authored the email w/o an image, that does not mean a service like sendgrid didn't add something to it (aside from 'received:' header info). -> You need to grab a copy of it post-delivery and examine email body source to be sure. If SA found an image more than likely there is an image. Look for " – B. Shea May 08 '18 at 14:51
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Sometimes there are hidden image beacons embedded in emails so they can be tracked. SendGrid, for example, does this, as most email services do.

Doug D Smartlab Software

Doug D
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  • Also seen this with some clients and services that incorrectly handle secure mail protocols like smime or PGP, whereas the armored output is mistaken as an image or the randomness appears as an attempt to bypass text filters as the message indicates. – linuxdev2013 Mar 23 '17 at 06:39