REPLY TO ALL: Am I Being Overly Paranoid About Spam Filters When Writing My Subject Lines?

Both SubscriberMail and Blue Sky Factory recently released lists of words that shouldn’t be used in emails because they’re likely to trigger spam filters. But I see some of these words—like “free” and “discount”—used routinely in the subject lines of commercial email that I receive. If I have a good reputation do I need to worry about content filters? Am I staying away from these words unnecessarily? —S.G.

The Voices of Email had this advice:

J.F. Sullivan: The answer should be no. If you have a good reputation then you do not need to worry about content filters. The actual answer is another question, as in it depends on two things: What’s your definition of a good reputation, and which content filter are we talking about?

Everyone in the email marketing (and message security) ecosystem has a different view of what a good reputation actually means. For some it’s as simple as making sure they are not on a blocklist; for others it may be that they are in compliance with a specific Sender Authentication implementation. In order to answer “yes” to the question, it may be more useful to provide a checklist summary of what a good reputation constitutes. So, if you can say “yes” to the following reputation aspects:

1. You have a good public reputation (not on blocklists, or have upset any ISPs).
2. You have good legislative adherence (e.g., CAN-SPAM compliance).
3. You have good infrastructure (e.g., DNS, MX records and the like).
4. You have good identity (e.g., you have a correctly configured SenderID record).
5. You have best practices (e.g., list scrubbing, opt-in, etc.).

…then yes, you do have a good reputation so you will not need to worry too much about content filters. And while your good reputation will work, say, 80% of the time, your actual delivery will still depend on the content filter you encounter to some degree. A subject of much longer blog entry for another day…

Rob Fitzgerald: You always need to be aware that filtering exists, but I don’t think you need to be ruled by that existence either. It’s interesting to lay out all the various releases, of all the various words that shouldn’t be used within in an email, and see how incredibly long that list is. Sometimes it makes me wonder how you can actually put a string of sentences together without actually using any of them. Practically speaking, you have to use some words that may be “known” filter words. I don’t think that should give you pause to run the campaign for fear of a lack of response. We’ve sent out many campaigns with the word “Free” on them that have performed very well.

I tend to look at it this way—it’s all about moderation. Put together a creative with a lot of words that trigger filtering and it could be adversely affected. Give that same creative a diet, and keep some of those same words included, but not all of them, and I think you’ll be OK.

Stephanie Miller: Despite the frequency that I receive this question, there is still no magical list of words to avoid, nor is the use of marketing terms like “free,” “discount,” “special offer” and “click here” an automatic block. Don’t misunderstand. Those words can get you blocked. However, judicious, responsible and clear use of them usually won’t.

Why? Because spam filters dynamically update to reflect current market conditions and spammer behavior. The only way to ensure your content does not depress inbox deliverability is to run every email through a series of popular message filters to determine your spam score before sending to your entire mailing list. You can do this through a service or on your own by setting up multiple accounts at different ISPs.

Here’s how to optimize your message for response and deliverability: Write the copy as a marketer. Sell. Build the relationship. Clarify the offer. Make the call to action very clear. Then, test it. If you fail the spam filters, adjust it. Before you hit send, even if you pass the filter test, be sure to give your message AND subject line a “smell test.” If your readers or subscribers will think it’s spammy, so will the receivers. If you are using all capped, repetitive words that filters watch like “FREE SHIPPING THAT’S FREE” or using strange punctuation like ***NOW ON SALE***, then you are likely to be blocked.

Chad White: Inspired by this question, I did a little real world research and found that major online retailers have used many of the “dirty” words on SubscriberMail’s list of words to avoid using in subject lines. How many have they used? They’ve used 27 of the 100 in the past two months alone. Some of the words—like “Free,” “FREE,” “Offer” and “Buy”—they used a LOT. So it’s clearly possible to use these no-no words in subject lines under the right conditions. Based on that I’d say that you should explore using them but test to make sure your emails are getting through.

Have some good advice that we missed? Please add a comment and take part in the conversation.

Have a question for the Voices of Email? Email Chad your question at and we’ll REPLY TO ALL by posting the answers so everyone can benefit.

–>Read other Reply to All posts

2 thoughts on “REPLY TO ALL: Am I Being Overly Paranoid About Spam Filters When Writing My Subject Lines?

  1. Emily,

    The amount of spam email you personally receive also has many variables – what ISP or Web mail provider you use; what email client you use; if you use an after market spam filter; is your email address posted on Web sites and being harvested by spammers, etc.

    I use Gmail for personal email and get almost no spam emails in my inbox – maybe 1-2 per week; while getting hundreds in the Gmail spam folder. Work is a different story – I get 300-400 or more spam emails a day – about 50-100 of them in my inbox, the rest in my junk folders. The difference between my Gmail account and work account is two fold – the difference in how Gmail filters versus our work email provider and the fact that my work email address is posted in many locations and harvested like crazy.

    Having a good sender reputation will greatly increase deliverability for legit marketers – but poor flitering by your ISP or email provider allows the bad stuff in to your inbox.

  2. Unfortunately, the answer is as varied as the security solutions in the market place multiplied by the ways to get the email delivered. Certainly, if you are still getting email with the subject line of "FREE SEX" then your spam filter is awful and needs to be replaced.

    That said, you are obviously pointing to a larger problem around authenticated senders and how illegitimate email is still getting into your inbox, if reputable senders are following the rules. A pithy answer is that the methods used by spammers to penetrate security solutions are always evolving; usually faster than their associated security solutions. That, and the fact that neither SenderID or DKIM is authenticating a majority of the email being sent….or that Goodmail has not managed to install its solution at >80% of the sending MTA in the world! 🙂

    Consider the following evolutionary path:

    Subject: SEX, VIAGRA, FREE
    Solution: Search for SEX, VIAGRA, FREE

    Subject: Sex, ViaGra, FrEe
    Solution: Search for mixed cases of Sex, Viagra, and Free

    Subject: S*e*x, V1agra, 5ree
    Solution: Search for "intentional" misspellings of Sex, Viagra and Free

    Etc., etc., etc.,

    Subject: Your Dad said to look at this…
    Attachment: dadsadvice.pdf
    Inside the PDF?: SEX, VIAGRA, FREE
    Solution: Detach, quarantine, etc. PDF attachments

    My point is that the fact that content (be it subject, body or attachment) may still as indelicate as it was 8 years ago is simply a reflection of the fact that an unfortunate group of people will click on those emails and spammers know that. Therefore, they do everything they can to make sure that they use those words, that content, to promote in their mailings. They bypass the spam filters by supporting authentication (at least SenderID), they use additional, superfluous content to confuse the content filtering algorithms, etc., ad nauseum. The spam filters continually have to adapt to these tactics and therefore you continue to get email that has obvious spam content.

    Consider the question you didn??t ask however. That is, why is it that Reputable emailers get blocked when they send email that contains certain catch phrases or words if the security solutions are constantly changing their detection to match the spammers? The answer to that is actually much simpler??the security solutions (as a sweeping generalization) rarely throw any specific tactic away because spammers have a habit of reusing old tactics in random ways to probe what the security solutions are capable of. So, SEX, VIAGRA, and FREE are searched by the security solution in the example above for??ever.

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