If you send regular emails—newsletters, announcements, or promos—you know the subject line makes or breaks your open rate. But “best practices” are all over the place, and what works for some list might flop on yours. If you want real answers, not just guesses, you need to run a proper A/B test. That’s what this guide is about: using Letterfriend to run simple, honest experiments on your subject lines, so you can stop guessing and actually improve your open rates.
This is for anyone who manages an email list, whether you’re a solo founder, marketer, or just the “email person” at your job. No snake oil, no fluff—just what you need to know to run better A/B tests with Letterfriend and get real results.
Why Bother with A/B Testing Subject Lines?
Look, you can write clever subject lines all day, but if you’re not testing, you’re just hoping. Here’s why you should A/B test:
- Your audience is unique. What worked for someone else’s list might not work for yours.
- Small changes can mean big differences. Sometimes adding an emoji or tweaking a word boosts opens by 10%—sometimes it does nothing.
- Gut feeling is overrated. Even seasoned copywriters get it wrong more than they’d like to admit.
- Data beats opinion. Testing gives you proof, not hunches.
But A/B testing can be a pain if your tool makes it complicated. That’s where Letterfriend comes in: it’s built to make this dead simple.
Step 1: Get Ready—What You Need Before Testing
Don’t just jump in and test for the sake of testing. Here’s what to have in place first:
- A decently sized list. If you’ve got 100 subscribers, you probably won’t see meaningful results. A few hundred is a minimum; a few thousand is better.
- A reason to test. Are your open rates dropping? Are you launching something new? Testing for no reason is a waste of time.
- A clear goal. Be specific: “I want to see if using the recipient’s name increases opens,” not “I want subject lines to be better.”
Pro Tip: If you’re not sending emails regularly yet, focus on that first. Consistency matters more than tweaking subject lines endlessly.
Step 2: Come Up With Subject Lines Worth Testing
Don’t test tiny tweaks; test real differences. Here’s what to try:
- Completely different angles. Example: “Your June report is ready” vs. “You’ve got results—see inside.”
- Personalization. Try adding the subscriber’s name or location.
- Urgency or curiosity. “Last chance to RSVP” vs. “Did you see this yet?”
- Short vs. long. Sometimes “Quick update” beats “Here’s everything you need to know about our June offering.”
What to skip: Don’t waste time testing “!” vs. “.” or changing one word unless you’ve already found a winning style and want to fine-tune.
Step 3: Set Up Your A/B Test in Letterfriend
Here’s how to do it without getting lost in the weeds:
- Log in to Letterfriend.
- If you’re not set up yet, get your account and mailing list imported. (Don’t worry, they walk you through it.)
- Create a new campaign.
- Choose your audience or segment.
- Choose “A/B Test” for subject lines.
- Letterfriend makes this obvious in the campaign setup. Pick “A/B test” when setting up your subject line.
- Enter your two (or more) subject lines.
- Don’t go wild with five variants; two is enough for most cases. More variants mean smaller groups and murkier results.
- Set the test parameters.
- Most users should stick with the default: send to a random sample (say, 20% of your list) for each subject line, then send the rest to the winner. If you want to get fancy, tweak the percentages, but don’t overthink it.
- Preview and schedule.
- Double-check your email content—A/B tests are only about subject lines, so everything else should stay the same.
Pro Tip: If you’re nervous about annoying your audience, remember: only a portion of your list sees the “loser” subject line.
Step 4: Let the Test Run—And Don’t Get Impatient
- Wait for enough data. Letterfriend will show you open rates for each subject line as people start opening. Don’t call it early—wait at least 24 hours, ideally 48.
- Don’t get distracted by tiny differences. If subject line A gets 28% opens and B gets 27.5%, that’s noise, not a win. Look for meaningful gaps (2%+).
- Ignore click rates for subject line tests. For this test, you care about opens, not clicks. (Clicks matter, but that’s a different experiment.)
What not to do: Don’t keep re-running the same test or tweak tiny things just to “optimize.” Run a test, learn, move on.
Step 5: Pick the Winner (Honestly)
Letterfriend will show you which subject line did better. Here’s how to decide:
- Is the difference real? A 5% gap is worth paying attention to. A 0.5% gap isn’t.
- Is the sample size big enough? If only 30 people opened, you don’t have a real answer—test again with a bigger group.
- Is it repeatable? If a certain style wins, try it again next time. Don’t assume it’ll always work—audiences change, and so do moods.
Don’t let your ego get in the way. If your “clever” subject line lost, accept it and use what works.
Step 6: Apply What You Learned (and Rinse, Repeat)
You’ve got a winner—now what?
- Use the winning style in your next campaigns. Don’t just copy-paste the exact line every time, but stick with what’s working.
- Keep a simple record. Jot down your test results somewhere. Over time, you’ll spot patterns (or see that what “works” changes).
- Test again, but not every week. You don’t need to run an A/B test with every email. Try it once a month, or when you’re launching something big.
Pro Tip: Don’t try to “game” your open rates with clickbait. If your subject line tricks people, your unsubscribe rate will spike, and your deliverability can tank.
What Works (and What’s Overrated)
What Actually Works
- Clear, honest subject lines tend to beat clever ones over time.
- Personalization can work, but only if it feels natural.
- Urgency works for offers, but can backfire if overused.
- Curiosity is good, but don’t be vague to the point of annoyance.
What to Ignore
- Trends like “add a rocket emoji to everything” rarely hold up.
- Endless micro-tests. Test big ideas, not punctuation.
- Obsessing over every percentage point. If your open rates are solid, focus on your content and list health.
Keep It Simple—And Don’t Sweat the Small Stuff
A/B testing subject lines with Letterfriend is straightforward if you don’t overcomplicate it. Test real differences, use the data, and don’t get precious about your favorites. Email is about building trust, not tricking people into opening something they didn’t ask for.
Keep your tests simple, your expectations reasonable, and your focus on what matters: sending emails your audience actually wants to open. Iterate, learn, and move on. That’s how you actually get better—and keep your sanity.