Does sizzle = fizzle for you subject lines?

I’m not surprised that you’re worried about your subject lines. Here’s a scary statistic: According to EmailToolTester, 11.1% of all emails sent never reach the inbox thanks to deliverability issues. And that’s just the average. In some industries, it’s much, much higher. 

Is it happening to you? 

Spam triggers are the obstacles standing between you and your reader’s inbox. In our increasingly automated world, email service providers rely on words, phrases, and expressions to generate red flags. And those red flags get you sent straight to the promotion folder or (even worse) into the dreaded spam folder.

And sometimes, it’s the sexiest messaging that winds up being the biggest offender. 

While it can be virtually impossible to know every single word or phrase that will get your content red-flagged, that doesn’t have to be the end of the story. You can take some simple steps to prevent some of the most common triggers from slipping through your editing process. 

The 5 Main Spam Filter Categories

That starts with knowing the five main categories of spam vocabulary that email service providers guard against. 

  1. Words associated with urgency
  2. Shady or unethical words and phrases
  3. Exaggerated claims that overpromise
  4. Pretty much anything that has to do with money, income, or cash
  5. Finally, the ever-tricky “unnatural” category

It doesn’t take more than a quick glance at these to see why so many sexy offers wind up straight in the spam folder, does it?

Now, keep reading to find out what you can do about it.

If it makes you feel any better, this is a tough lesson most of us have to learn the hard way. I’ve been guilty of some doozies myself. In one of our news-focused newsletters, I had a sexy subject line on a breaking story about the fentanyl crisis. Except I used the word “fentanyl” in the subject line. Which practically every email client I sent to interpreted as a violation of Category #2. And for about three days, they punished me for it. 


This led to the discovery of a stellar hack that helped outsmart spam triggers in 2022. It highlights more than 750 words and phrases that will probably land you in the spam folder. And what’s terrifying is how many of them you’re probably using with abandon. 

You can take a look at it here.

So, here’s the bad news: while this exhaustive list can help you identify words and phrases that are making ESPs everywhere hate you and your sends, that’s all it does. 

Once you’ve identified the offending words and phrases that have crept into your copy, what then?

Here’s What You Do Next

That’s when it’s time to bust out the thesaurus and get busy. 

Since you can’t say “act now” without getting punished, what else could you say? “This is what you need to do this second” is a powerful (if a bit longer) alternative. So is asking, “What are you waiting for?”

The point is, once you know the rules, you can figure out better ways to bend and break them without getting punished.

Bookmark this list so you can refer to it later. Evaluate the copy and subject lines of the last three emails you sent that totally bombed. Do any of those trigger words clue you in about where you went wrong? Get busy thinking of clever ways to reword that content so you can inbox better.

Exceptions to the Rule

If you have your heart set on a subject line with a whole lot of sizzle, there is a workaround.

If you have a stellar email reputation, email clients will often let things slide.

As long as your readers are highly engaged and not complaining. 

Or, you can utilize triggered sends to get those sexy subject lines out without being punished. The same subject line that will get you filtered in a blast can make it through on a triggered send.

Again – once you know the rules, you can get away with breaking them!

If open rates and inboxing really matter to you, there’s one surefire way to increase your open rates to 50-70%: putting Inbox Mailers to work. “Once we saw the initial numbers, we were hooked and on the Network the following week. The results are fascinating and our deliverability team is loving the lift across all of our sends.” That’s how Inbox Mailers changed the game for one of our users. How can it help you change yours?

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John Gardner

John Gardner is an expert email marketer and co-founder of Inbox Mailers. He specializes in email segmentation and improving overall deliverability, helping top brands and businesses optimize their email marketing strategy.