If your open rates are dropping and your emails are quietly slipping into spam folders, you’re not alone. Even marketers with well-segmented lists and beautifully designed emails can get caught by spam filters—and often, it all starts with the subject line.
In the early 2000s, avoiding the junk folder was mostly about language. Certain words, “FREE,” “Act Now,” “Earn $$$”, practically guaranteed you’d end up in spam. We all had our trusty cheat sheets. But things have evolved. Spam filters are now smarter, scanning everything from your domain reputation to user engagement.
That said, subject lines still matter. A lot.
Even with solid infrastructure and a clean, opted-in list, the wrong combination of words can still hurt your deliverability. Let’s dig into what those words are, why they still matter, and how to write subject lines that actually get opened, and build trust.
Spam trigger words are phrases that set off alarms with email service providers. These terms became infamous back when filters relied heavily on content-based rules to flag junk. Think “Buy Now” or “100% Free.”
Today, filters are more sophisticated. They consider sender reputation, authentication protocols, engagement history, and even user behavior. But here’s the thing: when those factors aren’t perfect, spammy language can tip the scales against you.
So if your list isn’t highly engaged, or your domain authentication is lacking, even one sketchy subject line can land your email in trouble.
There’s no universal “do not use” list, but certain categories of words and phrases show up again and again in emails that get flagged or filtered.
Financial promises are a big one. Subject lines like “Earn extra income,” “Work from home,” or “Get paid instantly” often trigger filters, especially if they lack context or feel too good to be true.
Urgency is another common culprit. Saying things like “Act now!” or “Limited time only” can backfire when overused. If everything’s urgent, nothing is.
Freebie language is also risky. Subject lines like “Free gift,” “50% off,” or “Claim your prize” might sound enticing, but they also read like classic spam. You don’t have to avoid offering something valuable, just don’t frame it like an infomercial.
Misleading phrases are another red flag. “You’re a winner!” “Important account update.” “This isn’t spam.” These types of lines might grab attention, but they scream clickbait, and filters know it.
Medical or legal claims should also be handled carefully. Anything promising a cure, legal advice, or a “fast solution” without the right context can raise suspicion fast.
And finally, there’s sensationalism. Lines like “Shocking deal,” “You won’t believe this,” or “Secret revealed” may have worked in 2005, but today, they just look shady.
The goal isn’t to write bland emails. You can still use strong, clear, even edgy language. But you have to make sure your backend setup is doing its part.
Start with domain authentication. SPF, DKIM, and DMARC might sound technical, but they’re essential. They prove to inbox providers that your emails are coming from a verified source. Skip this step, and your emails start with a trust deficit.
Next, monitor your sender reputation. If subscribers are ignoring your messages or marking them as spam, inbox providers will take notice. Tools like Google Postmaster Tools and Cisco Talos can help you track how your emails are being received.
Then there’s engagement. It’s the strongest trust signal you have. When people are opening, clicking, and replying, your reputation improves. If they’re deleting your messages or letting them sit unopened, your next campaign may never reach the inbox.
And if you really want to stand out?
That’s where BIMI comes in.
BIMI (Brand Indicators for Message Identification) allows your brand’s logo to appear directly in supported inboxes like Gmail and Yahoo. But it’s not just a visual feature, it’s a badge of trust.
To qualify for BIMI, you need full DMARC enforcement (not just monitoring), an SVG version of your logo hosted in your DNS records, and a Verified Mark Certificate (VMC), which Gmail requires for displaying your logo.
It’s a strong visual signal that says, “This sender is legitimate.” And in a cluttered inbox, that kind of credibility can lead to better open rates, higher engagement, and improved brand recognition.
Think of it as showing up to your customer’s inbox with a verified checkmark and a friendly face, while your competitors show up anonymous.
Let’s say your subject line reads: “Get Out of Debt Now!” It’s direct, but also raises red flags. Try reframing it as: “Smarter Ways to Lower Your Monthly Bills.” It’s still helpful, but less aggressive.
Maybe you’ve written: “URGENT: Your Gift Inside.” That kind of language has been overused by spammers for years. Instead, try: “A Small Thank You, Just for You” or “We Thought You’d Like This.” It’s warm, personal, and still sparks curiosity.
And if you’re thinking about using “You’re a Winner!”, don’t. A better approach might be: “Thanks for Being Part of Our Community.” It still feels good to receive, but it won’t raise the same red flags.
Simple. Honesty. Clarity. Relevance.
Your subject line should reflect the real content of your email. Give people a reason to open, not by tricking them, but by offering value and setting expectations.
The best-performing subject lines don’t hack the system. They align with what your reader wants and what your brand actually delivers.
Because inbox placement isn’t just about technical compliance, it’s about relationship. The more your audience trusts you, the better your emails perform. And that trust starts the moment your subject line appears on their screen.
If you’re not sure whether your subject lines are helping or hurting your deliverability, let’s take a look together.
We’ll review your email setup, your content, and your strategy, then show you how to fix the things that are quietly sending your messages to spam.
Schedule a time to speak with us and make sure your next campaign lands where it belongs: in the inbox.