Here's the uncomfortable truth: word choice matters less than you think. According to InboxEagle's Q1 2026 analysis of 774,828 emails, messages containing discount words like "free," "sale," or "% off" had a 21.7% spam rate — while emails with no discount language at all sat at 22.7%. That's right: emails with discount words actually performed slightly better.
A quick caveat before you run with those numbers: InboxEagle's dataset skews heavily toward e-commerce and marketing email senders — think flash sales, "% off" campaigns, and purchase-intent lists. That's a different animal from cold B2B outreach, where you're contacting people who never opted in. The directional finding still holds, but the absolute spam rates may not map directly to your situation. InboxEagle is also a commercial deliverability vendor, so treat the data as useful signal, not gospel.
With that context in mind, here's what the data actually shows. When you drill into individual trigger words, the precise baseline for emails with none of these phrases is 22.56%. Against that baseline:
- The word "free" comes in at 24.28% — about 1.7 percentage points above baseline. Worth being cautious about, but not the catastrophic jump spam-filter mythology predicts.
- "sale" clocks in at 23.63% — slightly elevated but not dramatic.
- "% off" actually performs better than the baseline at 20.46%. Specific, numeric discount language is apparently safer than vague promotional copy.
The broader bucket-level headline — 21.7% for all discount-word emails vs. 22.7% for none — tells a similar story. The conventional "avoid sale language" advice is aimed at the wrong variable.
Why does "free" carry more risk than "% off"? It's not the word itself. It's the audience. "Free" tends to appear in broader, less targeted sends going to larger, less segmented lists with more unengaged subscribers. Those disengaged contacts are the ones hitting "Report spam." ISPs aren't pattern-matching keywords — they're reading your complaint rate, engagement signals, and authentication setup.
What actually matters more:
- Sending infrastructure. If you're blasting cold emails from an unauthenticated domain, no amount of word scrubbing will save you. According to Validity's 2024 Email Deliverability Benchmark (as reported by MailReach, a deliverability vendor), roughly one in six emails never reach the inbox globally. Note that MailReach sells warm-up and deliverability tools, so factor that in — but the underlying Validity benchmark is widely cited.
- Plain text over HTML. Cold email should be plain text. HTML emails carry more spam signals and look like marketing blasts, according to Puzzle Inbox's breakdown of how spam filters score emails.
- Signal stacking, not single words. Modern spam filters use score-based systems. One "free" rarely crosses the threshold alone. Using five to ten spam-flagged words stacks signals quickly and that's when you're in trouble, per Puzzle Inbox's analysis.
- Context over vocabulary. Words like "urgent," "limited time," "guaranteed," and "click here" are still worth avoiding — not because they'll individually tank your deliverability, but because they're associated with spammy sending patterns that correlate with poor engagement.
So yes, keep "free," "get rich quick," and "buy now" out of your subject lines — especially if you're sending to cold lists where engagement is already an uphill battle. But stop treating trigger words as the root cause. The problem is usually deeper: your sending infrastructure, your authentication setup, and whether you're sending to people who have any reason to care about your message.