Spam trigger words to avoid used to be the whole game, filters in the early 2000s worked almost entirely off word lists, and while modern filters at Gmail and Outlook rely much more on sender reputation and behavior now, certain words are still disproportionately represented in spam training data, which means they still nudge a message in the wrong direction, especially stacked together. Here's the list I flag most often, and why each one still matters.
Modern spam filters are pattern-based, they're weighing sender reputation, authentication, engagement history, and content together rather than scanning a word list and rejecting on match. But the content signal hasn't disappeared, it's just one input among several, and certain words show up so heavily in historical spam and phishing data that filters still weight them, particularly when they appear alongside other red flags like poor authentication or a cold sending domain.
The practical takeaway is that one flagged word in an otherwise well-authenticated, well-engaged send probably won't hurt you. A subject line stacked with three or four of them, sent from a domain with shaky SPF and a stale list, is a different story, since now every signal is pointing the same direction.
I'd also separate two different risks that get lumped together under "spam trigger words." One is landing in the spam folder outright, which is mostly driven by reputation and authentication with content playing a supporting role. The other is getting swept into Gmail's Promotions tab, which leans more heavily on exactly this kind of promotional language, so if your mail is consistently landing in Promotions rather than spam, trimming these words matters more than it would for a straight spam problem.
None of these need to disappear from your vocabulary entirely, "free shipping" in a normal ecommerce email is fine, it's the combination of the word with aggressive formatting and a thin sender reputation that turns it into a problem.
These phrases read as pressure tactics because that's exactly what they've historically been used for, and filters trained on years of that pattern still recognize it quickly.
Words are only half of it, formatting compounds the signal. ALL CAPS SUBJECT LINES, three or more exclamation points, dollar signs used as decoration ($$$), and excessive emoji stacked in a subject line all read the same way to a filter as the word list above, they're patterns strongly associated with spam and low-quality marketing mail, and combining them with a flagged word makes the whole message look worse than either alone.
The same logic carries into the body of the email, not just the subject line. A message that's mostly one large promotional image with a few lines of disclaimer text, or one packed with tracked links pointing at a dozen different products, reads as automated regardless of which words you avoided in the subject. Filters and Gmail's Promotions classifier both look at the whole message, so cleaning up the subject line while leaving a heavily templated, banner-driven body behind only solves part of the problem.
The better move isn't memorizing a banned word list, it's writing subject lines the way you'd actually describe the email to a friend, specific and a little understated rather than hyped. "The three tools I used to fix my list" beats "FREE tools that will change your business!!!" on every metric that matters, opens, replies, and staying out of spam. I've put together a full breakdown of how to write catchy subject lines that lean on curiosity and specificity instead of urgency words, and if you want the fuller list of what to fix beyond subject lines, how to stop emails going to spam covers the rest of the stack.
Rarely on their own, modern filters weigh sender reputation and engagement much more heavily, but trigger words still add to the overall pattern a filter is scoring, especially on a domain with weaker reputation.
You can use it, plenty of legitimate emails do, the risk goes up when it's paired with aggressive formatting like all caps or multiple exclamation points and sent from a domain with poor sender reputation.
Yes, cold email starts with less trust since there's no prior opt-in relationship, so the same trigger words carry more weight than they would in a newsletter to an engaged, opted-in list.
The free Inbox Scorecard flags content and authentication issues together, so you can see whether wording is even your real problem before you rewrite anything.