Latest / The Email Marketing Podcast with Fexingo: Newsletters, Open Rates, and Subscriber Growth / How One Subject Line Boosted Open Rates by 31 Percent
Transcript
- Lucas: So there's this stat that's been bouncing around my head all week: a mid-sized e-commerce brand — think home goods, not a household name — lifted their open rates by 31 percent just by rewriting their subject lines. No list growth, no send-time changes, no new offers. Just the words in that little box. Luna: Thirty-one percent is huge. But how much of that is just the novelty of trying something new? You run a test, anything changes, and you see a bump. Lucas: That's the right question, and it's exactly why they didn't just do one test. They ran a sequence of experiments over eight weeks, each one isolating a single variable — length, personalization, emojis, and the most interesting one, what they called the curiosity gap. Luna: Curiosity gap — that's the idea that you leave something unsaid, make the reader want to click to find out. Like 'We need to talk about your order' but less ominous. Lucas: Right, but the key is it has to be honest. This brand's winning subject line was, 'The one thing we changed about our shipping' — and the email actually explained a small but real improvement they'd made to their packaging. The gap wasn't a trick; it was just revealing the benefit at a slower pace. Luna: So it's not clickbait, it's delayed gratification. That's a much more sustainable approach. But how did they measure the 31 percent? Was that against their old average, or a controlled group? Lucas: Great point. They compared the new subject lines against their previous 12-month average, but they also ran holdout tests where part of the list got the old style. The 31 percent was the delta between the new and the old in the same send window. So it's pretty clean. Luna: That's solid. And I'm guessing they didn't just change one thing—they probably stacked multiple techniques. How did they break down the individual contributors? Lucas: They did. The biggest single lift came from the curiosity gap — about 18 percentage points of that 31. Then personalization, like using the recipient's first name or a product they'd browsed, added another 9. And the remaining 4 came from trimming subject lines to under 40 characters. Luna: Interesting. So personalization is still powerful, but not as powerful as that narrative hook. I've seen brands overdo personalization to the point where it feels creepy. Did they hit any of that? Lucas: They actually had a cautionary tale built into the same experiment. A test with a subject line that referenced the recipient's abandoned cart item by name — 'Hey Sarah, your lavender diffuser is waiting' — actually underperformed the generic version by 7 percent. Their audience found it too specific, too intrusive. Luna: That's a great reminder that personalization isn't always better. Context matters. The trust level with your brand, the type of product, the stage of the relationship. Lucas: And that's where segmentation comes in. They applied the curiosity gap to their most engaged segment — people who'd opened at least five emails in the past three months — and saw a 22 percent open rate. On their cold segment, the same subject line style only got 11 percent. Same words, totally different response. Luna: So you can't just copy a winning subject line and expect magic. It has to match the audience's familiarity with you. For a cold list, you probably need to lead with a clear value proposition, not a mystery. Lucas: Exactly. And that's what I love about this case — it's not a silver bullet, it's a process. They tested, they segmented, they learned. Which, honestly, is the real takeaway. And it's why we love digging into these numbers on the show. Luna: Yeah, and speaking of that — we're able to keep these episodes ad-free because of listeners like you who chip in a coffee now and then. If these marketing experiments have sparked something you've tried in your own campaigns, supporting the show at buy me a coffee dot com slash fexingo helps us keep the conversation going without interrupting it with ads. Lucas: That's exactly it. It's a small way to say 'this matters to me,' and it directly keeps the podcast independent. No pressure, just appreciate the thought. Luna: So back to that 31 percent. What did they do after the initial win? Did they just stick with the winning formula, or did they keep iterating? Lucas: They kept iterating, which is the smart move. They took the winner and started A/B testing the next layer — like whether using a number in the subject line outperformed a word. '3 reasons' versus 'three reasons' — the numeral won by 6 percent. Small stuff, but it compounds. Luna: That's the compounding effect of optimization. But I'm curious about the long-term. Did that 31 percent hold up over time, or did the novelty wear off? Lucas: Six months later, their open rates were still 18 percent above the baseline. So they lost some of that initial boost, but they retained more than half of the gain. And their click-through rates actually went up 9 percent, which suggests the curiosity gap wasn't just tricking people into opening — it was attracting the right kind of engagement. Luna: That's a healthier metric to chase. Open rates can be gamed, but if clicks improve, it means the content delivers on the promise. Did they see any impact on unsubscribes or spam complaints? Lucas: They tracked that carefully. Unsubscribes stayed flat, and spam complaints actually dropped by 12 percent. Their theory is that the curiosity gap created a stronger expectation of value, so subscribers were more forgiving if an email didn't resonate. They felt less 'tricked' because the subject line wasn't overpromising. Luna: That's a really nuanced outcome. It's not just about opens — it's about trust. And that's something you can't buy with a tool. Lucas: Right. And the other thing they did was apply the same principles to their transactional emails — order confirmations, shipping updates. Those usually have sky-high open rates anyway, but they added a curiosity gap to the 'your order is on its way' email and saw a 15 percent increase in clicks to their product recommendations. Luna: Smart. You already have their attention, so you use that moment to deepen the relationship. That's the kind of high-leverage play that most brands miss. Lucas: Absolutely. And the final piece of their strategy was documenting everything in a subject line playbook for their team. They have a live document with 'wins,' 'losses,' and 'hypotheses,' so every new marketer can learn from their data instead of starting from scratch. Luna: That's the kind of institutional knowledge that builds a durable advantage. It's not just a one-off test — it's a culture of experimentation. Lucas: Which is exactly what we'd recommend to any team listening: don't chase a single winning subject line; build a system that keeps learning. That's how you turn a 31 percent boost into a permanent edge. Luna: And if you're just starting out, the first step is to look at your own data. What's your current open rate? What patterns do you see in your top performers? That's where you begin. Lucas: Good place to start. Next time you're about to hit send on a campaign, ask yourself: is the subject line earning the click, or just demanding it? That question alone might be worth a 31 percent lift.