Yes, You Can Put “Free” In Your Subject Line

Thursday, Yahoo! released an email visualization tool. Updated every second, it shows the volume of email being delivered through Yahoo! users across the globe.

Click on the map, and it’ll zoom in to a breakdown of emails in that area (with all emails anonymized). Keep clicking, and it’ll display fascinating facts about Yahoo!’s user base.
You can also choose to either show or hide blocked spam messages.



But the visualizer’s not just fun to look at (though we’re crossing our fingers this is available as a desktop background very soon). If you click on the green “trending keywords” box, you’ll see something very helpful for email marketers:

The Current Top Words in Email Subject Lines

In blue, you see the most common words in subject lines hitting inboxes by the second (though the data’s delayed by about an hour).

Then, if you click the green “show spam keywords” box, you’ll see a gray representation of subject line words for emails being blocked as spam (though probably not for the subject lines).

So How Can You Use This?

Now, we’re not suggesting you start copying and pasting lists of safe words and danger words.

We’re suggesting that, once you get over the awe of this lovely tool, you take note of these two observations:

  1. Every time we take a look, the word “free” is hovering steadily in the “delivered” zone. “Free” subject lines are getting delivered. It’s safe.So no more typing fr.e.e in your subject lines, okay? For one, your subscribers must think your ring finger has a nervous tic. For another, it looks more suspicious than the real word anyway.
  2. If Yahoo is putting this information out there for anyone (spammers, desperate marketers, sane marketers and the general unconcerned populace) to see, they’re not worried about anyone gaming the system.

This suggests that the words you use in your subject line aren’t necessarily what flags emails as spam, and therefore, they aren’t the most important factor.

So instead of worrying exactly which words are “safe,” focus on which words are engaging and entertaining and make the sale.

Keep your focus on subscriber engagement, get whitelisted and work on building relationships – then watch your own subject lines show up in the Visualizer when you click the “queue” button!

Have You Explored Visualizer?

What do you think? Helpful, or just a digital lava lamp?

If you notice anything else about the visualizer that email marketers should know, please share in a comment below!


  1. Duncan

    10/18/2011 12:46 pm

    Great info! Thanks for sharing!

  2. Jose Dias

    10/18/2011 3:42 pm

    70k+ emails per second is amazing. Can you imagine how much they are paying to their email marketing service? I hope they signed up for an unlimited plan. :O)

    And it is good news to know that we don’t have to be so paranoid with the subject line. I agree that F.R.E.E and other variations are a turn off and I would never use them.

    Thank you for sharing.

  3. Justin

    10/18/2011 4:29 pm

    Very cool tool. Thanks for sharing. Been playing with it now for about half an hour so must stop!

  4. Carene

    10/18/2011 6:25 pm

    Thx Good to know!

  5. Gawie

    10/19/2011 4:19 am

    Thanks for all your tips it help a lot.

  6. Andrew Kordek

    10/22/2011 10:44 pm

    The Yahoo email visualization tool is like email marketers eye candy.

  7. Mel

    1/15/2012 10:17 pm

    I just looked and it had Free as a top Spam keyword now.

  8. Tommi Pryor

    7/31/2012 8:27 pm


    It’s not that the information provided in this article is wrong, it’s that it is incomplete and not presented in context. All of the major ISPs and email hosts use the open source progra, “SPAM ASSASSIN” algoryhthm as the backbone of their spam filters. They may customize and build upon it, but it is common to them all.

    Spam assassin uses a scoring system that assigns values from 1 to 5 to email charecteristics common to spam. These include, for instance, such things as “trigger” words used in subject lines and message body (such as “Free”, “Winner”, “Viagara”, etc.). These also include image-to-text ratio in the body (the algorhythm knows that human beings use mostly text in their personal communications as do businesses who aren’t spamming). In addition, this includes overuse of bold, undelined and colored type; colored backgrounds or background images; and use of punction, special characters and uppercasing in subject lines.

    It is NOT that you cannot use a “trigger” word like “Free” or boldface or underscore an important point in your message. However, each SPAM trigger present in the email will be assigned a number by the algorhythm as it scores all elements of the email in nano-seconds and then calculates the score. An email with a score of 0-2 is considered “safe”. An email with a score of 5 is going straight to the spam filter. Whether emails with a score of 3 or 4 make it to the in-box or get diverted to the spam filter depends on the “tolerance” level that the ISP or email host has customized its filters to. An individual email user’s settings preferences may also impact this.

    So, yes, a lot of emails that use “trigger” words like “free” in the subject line or body may make it into the in-box, likely because the balance of the email’s charecteristics do not include OTHER spam triggers–or not enough to raise the score above 2 or possibly 3. Therefore, it would be careless to say, “Go ahead and use “Free” or other trigger words liberally in your subject lines and message bodies without providing this context.

    Just think of like this: You go on a diet. The diet plan says you can have a nightly dessert. You say “Whoopee” I can eat a 1,000 calories dessert every night on this diet and I’ll lose weight! you conclude that because you read an article that told you that millions of people are on the same diet and are eating dessert and losing weight. But if no one puts that in context for by explaining that you will need to stay within 1,200 calories a day, and you continue to eat 1,200 calorie desserts daily–you will never reach your goal.

    So think of using trigger words (like “Free”) and other trigger characteristics as a 1,200 calories piece of chocolate cake. If you eat something with that many “points”, you might fail at your diet. If you understand that there is a 1,200 calorie limit, you might instead opt for that 200 calorie, sugar free pudding cup to keep your “score” in the safe zone. Think of the trigger factors you add to your mass emails as “calories” and stay in the safe zone with as few as possible (or none at all if possible).

    I always run the emails we send out for clients through the Lyris spam Scorer. This gives us an immediate report with a breakdown of what factors are factoring into the score and at what level. This gives us an opportunity to adjust anything we need to before we press “SEND.”

    Glad to help anyone who has additional questions!

  9. Amanda Gagnon

    8/1/2012 8:06 am

    Thanks for sharing Tommi. Of course, one factor (the use of “free” or not) won’t get you into the inbox or keep you out of it, and I appreciate your additional information provided here. The above article was simply meant to explain that the tool indicates that in Yahoo! inboxes, at least, subject lines with “free” are making it in quite a lot. But of course, other factors impact deliverability as well.