Many email marketers know now that just because you send it, that doesn’t mean it went anywhere. There are many factors that go into your deliverability – the science of whether or not your email makes it to the Inbox – one of which is the content of the email itself.

Last week, a client asked us if they would automatically get a one-way ticket to the junk or spam filter if they used “free” in the subject line. They’re thinking with the right mindset – content does matter! But, luckily for promotional email marketers, saying “free” once most likely won’t get you flagged as spam.

Whether you go to Inbox, junk folder or nowhere at all is up to each individual email filter (Outlook, Brightmark, Postini, Yahoo, etc.). From a content perspective, they each have different thresholds for what gets marked as spam. While Outlook’s junk filter may not mind you using “FREE” once in the subject line and twice more in the body of the email, Postini – a 3rd party spam filter – might.

The best way to find out what those thresholds are is to test your email content before you deploy it. In the emfluence Platform, you can send a “Pre-Flight Check” during the Preview step and test your email content against 9 of the most common desktop spam filters. Your results will come back in about 20 minutes, and if you see that you’re not passing one of the filters, you can try tweaking your content in order to pass. That may mean a small, simple modification like changing “FREE!!!” in 72pt font to “FREE!” in 24pt font. Or it may mean that you incorporate your large-font headline into an image – which spam filters can’t read – and let the text of the email balance out the content. (Reminder: using one big image as your email content is also usually bad for deliverability, so “hiding” all your promotional words in images won’t work either.)

Back to our client’s question: what about the subject line, though? Yes, the subject line is a little tougher, but only because the subject line is 80-characters maximum. So if “FREE” uses up to 4 of those characters, it represents a greater portion of the total subject line and can tip the balance more quickly. If you’re not passing spam filters in the Pre-Flight Check, try changing the body of the email to regain balance. Or try using “free” without the caps in the subject line, re-run your Pre-Flight check, and see if that makes the difference.

Have questions about the results of your Pre-Flight Check? Reach out to our sleuthing team at We love to figure out that tightrope-thin-line of what will pass filters, but still allow us to send effective promotional copy to our subscribers.

Interesting note: this blog post was shared in the June emsights email newsletter, with the word 'free' in its own subject line. One version of the email failed Outlook and Postini's filters and the final sent version passed. The only difference? Removing a tweet from the "reel" on the right hand column inside the email! Click on the thumbnails below to see the (small!) difference.

First try failed Postini & Outlook


Small tweak to remove one of the tweets on the right hand side allowed the email to pass spam filters!




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