Do “spam words” still matter?

In 2003, putting "FREE!!!" in your subject line was a fast track to the spam folder. Keyword blocklists ruled deliverability, and copywriters spent real energy rewriting around trigger phrases. That era is mostly over. But spam words aren't entirely irrelevant either, and the nuance matters if you're trying to improve inbox placement.

Modern spam filters use machine learning trained on billions of emails. They're primarily looking at engagement signals (do subscribers who receive your mail actually click?), authentication signals (is your SPF and DKIM in order?), and sender reputation (what's your spam complaint rate?). A phrase like "act now" or "limited time offer" contributes a small nudge to a composite score that's dominated by those other factors. On its own, it won't send you to the spam folder.

That said, certain phrases still correlate with spam in training data, so they can tip a borderline score in the wrong direction. If your authentication is solid, your list is clean, and your engagement is healthy, a promotional subject line won't hurt you. But if you're already in a gray zone on reputation, a subject full of classic spam phrases can be enough to tip the balance. The fix isn't to write bland copy to avoid trigger words. It's to fix the underlying signals: authenticate properly, remove inactive subscribers, and send content people want to click.

If you're worried your copy is triggering filters, the most useful test is a seed list run with an inbox placement testing tool like Litmus. That gives you real data on where you're landing rather than guessing based on word lists. Fix your authentication and list quality first if placement is off. Spam word optimization is near the bottom of the deliverability priority list, not the top.