If you’re sending emails for sales, outreach, or newsletters, you already know subject lines can make or break your open rates. But guessing at what works is a waste of time. A/B testing subject lines is the only way to know for sure what your audience actually responds to. This guide is for anyone using Nureply who wants to get real results—without the fluff or wishful thinking.
Let’s walk through how to set up an effective A/B test for your subject lines in Nureply, what to pay attention to, and a few traps to avoid.
1. Understand Why (and When) to A/B Test Subject Lines
A/B testing is simple at its core: you send two (or more) versions of an email—each with a different subject line—to similar audiences. You see which one gets opened more. It’s not magic, but it’s the most honest way to improve your open rates.
When should you A/B test? - When you have enough contacts. Testing with 50 people is pointless; you need at least a few hundred per variation to trust the results. - When you’re not sure what works. If you’re writing subject lines by gut feeling, it’s time to test. - When you’re trying something new: a new offer, a new segment, or a different tone.
When to skip it: - If you’re sending a one-off announcement to a tiny list. Just pick your best guess. - If you don’t have time to act on the results. Testing only matters if you’re willing to change.
2. Prepare Two (or More) Subject Lines
Don’t overthink it. The point isn’t to write the perfect subject line, it’s to learn what works for your list.
Start with two versions: - Version A: Your current “best guess.” What you’d normally use. - Version B: Something different—shorter, longer, more personal, asks a question, etc.
What makes a good A/B test? - Change one thing at a time. If you change the subject line and the preview text, you won’t know which made the difference. - Be bold, but not random. Test real ideas, not just minor tweaks.
Examples: - “Quick question about your hiring process” - “Looking for a new team member?”
Or
- “June newsletter: 5 tips for remote teams”
- “How remote teams are saving 10+ hours a week (June update)”
Don’t bother testing: - Subject lines that are almost identical (“Hi John” vs “Hi, John”). The difference will be noise. - Spammy tricks (“RE:”, “FWD:”, all caps). These might get opens but will hurt your reputation.
3. Set Up the A/B Test in Nureply
Nureply makes A/B testing subject lines pretty straightforward, but don’t get lost in the options. Here’s what actually matters:
Step-by-step:
- Create a new campaign (or edit an existing one).
- In the subject line area, look for the “A/B Test” or “Add Variation” button.
- Enter your two (or more) subject lines.
- Decide what percentage of your list gets each version. A 50/50 split is fine for most cases.
- Double-check that everything else in the email is the same.
Pro tip:
If you’re testing to find a “winner” and then want to send the rest of your list the best subject line, use Nureply’s automatic winner feature—if it’s available. If not, just check the results after your test group and roll out the winner manually.
4. Choose the Right Audience Size
More data means more reliable results. But you don’t need a PhD in statistics.
- Minimum: 200+ recipients per version. Fewer than that, and you’re just rolling dice.
- Ideal: 500+ per version, if you have it.
- If your list is small: Test over time. Do A/B tests on every campaign and look for patterns.
Don’t: - Test with your entire list if you’re using it to find a winner. Use a portion, then send the winner to the rest. - Obsess over tiny percentage differences (e.g. 24% vs 25%). Look for clear, meaningful jumps.
5. Send the Test—And Wait
Send your email and don’t peek at the results for at least 24 hours. Most of your opens will happen quickly, but some trickle in. If your audience is global, give it 48 hours.
Why wait?
Jumping to conclusions on early data is a classic mistake. Let the numbers settle.
6. Analyze the Results (Without Fooling Yourself)
Open rates are your main number here. Higher is better, but context matters.
Look for: - A clear winner. If one version is up by 5% or more, and you have a decent sample size, that’s real. - Consistency. If you run a few A/B tests and the same style keeps winning, you’ve found a pattern.
Ignore: - Tiny differences. A 1% or 2% gap probably isn’t real. - Click rates, unless your email content is also different. You’re testing subject lines, not body copy.
A/B testing myths: - “Winning subject lines work for everyone.” Nope. Your audience is unique. - “Test everything, all the time.” Not necessary. Test when it matters—a new campaign, a new audience, a big change.
7. Roll Out the Winner (and Document What You Learn)
If you’re happy with the winner, send it to the rest of your list. But don’t just move on—make a quick note of what worked. Over time, you’ll see patterns: maybe your list likes questions, or really short subject lines, or personalization.
Keep a swipe file:
Copy/paste your winning subject lines into a doc or spreadsheet. Review before writing new campaigns. This isn’t just busywork—it saves you time and keeps you honest.
8. What to Avoid: Common A/B Testing Mistakes
- Testing too many variables. Stick to one change at a time.
- Testing too often with tiny lists. You’ll get random results.
- Chasing “best practices” over your own data. What works for other companies might flop for your audience.
- Letting one test decide everything. Trends matter more than one-off wins.
9. Pro Tips for Better Subject Line Tests
- Shorter is usually better, but not always. Test it for yourself.
- Personalization can help—or not. “First name in subject” works for some, annoys others.
- Avoid spam triggers. Words like “Free,” “Urgent,” or excessive punctuation can land you in spam folders.
- Don’t be afraid to repeat tests. Just because a subject line won last month doesn’t mean it’s a winner forever.
Keep It Simple & Keep Testing
A/B testing subject lines in Nureply isn’t complicated, but it does take a bit of discipline. The key is to stay curious, don’t get tricked by tiny differences, and let real results—not guesses—shape what you send next. Keep it simple. Test one thing at a time. Save what works and keep iterating. That’s how you actually get higher open rates without chasing every new fad.