How Do I Write Subject Lines That Get App Users to Open My Emails?

A fitness app sends out their weekly workout reminder email to 50,000 users. The subject line reads "Weekly Workout Update #47" and gets a measly 2.3% open rate. The following week, they try "Your 5-minute energy boost is waiting" and suddenly 18% of their users are opening the email. Same app, same audience, but completely different results—all because of eight words.

If you've built a mobile app, you probably know that getting people to download it is only half the battle. The real challenge comes after—keeping users engaged, bringing them back, and making sure your app doesn't become one of those forgotten icons buried on page three of their home screen. Email marketing is one of the most powerful tools you have to fight this, but there's a catch.

Your email marketing campaign is only as strong as your subject line—if people don't open your emails, nothing else matters

Mobile app users receive dozens of emails every day, and they make split-second decisions about what deserves their attention. Your beautifully crafted newsletter about new features means nothing if your subject line doesn't make them tap. The stakes are high too—once someone starts ignoring your emails, it's incredibly difficult to win them back. Throughout this guide, we'll explore exactly how to write subject lines that cut through the noise and get your app users opening, reading, and most importantly, returning to your app.

Understanding Why Email Subject Lines Matter for Mobile Apps

Your app might be brilliant, but if users aren't opening your emails, they'll never know about your latest features, updates, or offers. The subject line is your first—and often only—chance to grab their attention. Think about your own inbox for a moment. You probably get dozens of emails daily, and you make split-second decisions about which ones deserve your time.

Mobile app users are particularly ruthless when it comes to email. They're busy people who installed your app for a specific purpose, and they expect your communications to add value to their experience. A weak subject line means your carefully crafted email content goes unread, your engagement rates plummet, and your users slowly forget why they downloaded your app in the first place.

The Numbers Don't Lie

Email open rates for mobile apps typically hover around 20-25%, which means roughly three-quarters of your users aren't even seeing your messages. But here's what's interesting—apps with strong subject line strategies often see open rates of 35% or higher. That's not luck; that's understanding what makes people tick.

What Happens When You Get It Wrong

Poor subject lines don't just hurt individual email campaigns—they damage your long-term relationship with users. When people consistently ignore your emails, email providers start treating your messages as spam. Your deliverability suffers, and even users who want to hear from you might never see your emails.

• Users start marking your emails as spam
• Your sender reputation takes a hit
• Email providers filter your messages to junk folders
• Engagement with your app decreases over time
• User retention rates drop significantly

The good news? Once you understand what makes subject lines work, you can turn these numbers around quickly. Your users want to hear from you—you just need to give them a reason to pay attention.

The Psychology Behind What Makes People Open Emails

After building mobile apps for years, I've noticed something interesting—the same psychological triggers that make people tap on your app icon also make them open your emails. It's all about understanding what drives human behaviour, especially when someone's scrolling through their inbox at lightning speed.

People open emails for three main reasons: curiosity, urgency, and personal benefit. That's it. When someone sees your subject line, their brain makes a split-second decision based on these factors. Will this email tell me something I need to know? Will I miss out if I don't open it now? What's in it for me?

The Mobile Mindset

Mobile app users behave differently from desktop users—they're usually distracted, multitasking, and have shorter attention spans. They might be checking emails whilst waiting for a bus, during ad breaks, or between meetings. This means your subject line has about two seconds to grab their attention before they swipe past it.

Fear of missing out plays a huge role here. If your subject line suggests there's something time-sensitive or exclusive waiting inside, people are more likely to tap. But—and this is important—it has to be genuine. Mobile users are smart; they can spot fake urgency from a mile away.

Keep your subject lines under 50 characters for mobile devices. Most email apps cut off longer subject lines, which means your carefully crafted message gets chopped in half.

The Emotional Connection

The best subject lines tap into emotions rather than logic. Words like "you," "your," and "free" work because they make the email feel personal and beneficial. Numbers also catch attention—our brains are wired to notice them amongst text.

Key Elements That Make Subject Lines Work for App Users

After working with hundreds of mobile apps over the years, I've noticed something interesting about subject lines that actually get opened. They all share certain characteristics that make them impossible to ignore—and it's not what most people think.

The most successful subject lines I've seen are short and punchy. We're talking 6-8 words maximum. Your app users are scanning their inboxes quickly, often on mobile devices, and they need to understand your message instantly. Long, rambling subject lines get cut off and lose their impact completely.

Personalisation That Actually Works

Using someone's first name isn't personalisation—it's lazy. Real personalisation comes from understanding how your users behave in your app. Subject lines that reference specific actions, achievements, or preferences perform much better. Think "Your workout streak is at risk" rather than "Hi Sarah, check out our fitness tips".

Creating Genuine Urgency

Urgency works, but only when it's real. Fake countdown timers and artificial scarcity will damage your reputation faster than you can say "limited time offer". Instead, use natural urgency that relates to your app's function—expiring content, time-sensitive features, or genuine deadlines.

Here are the elements that consistently drive higher open rates:

• Clear benefit or value proposition
• Action-oriented language
• Curiosity without being clickbait
• Relevance to recent app activity
• Emotional connection to user goals
• Mobile-optimised length

The best subject lines feel like they come from a friend who knows exactly what you need right now. They're helpful, timely, and respect your intelligence—three things that are surprisingly rare in most app email campaigns.

Common Mistakes That Kill Your Email Open Rates

After working with mobile app developers for years, I've noticed the same email marketing mistakes happening over and over again. The good news? They're all completely fixable once you know what to look out for.

The biggest killer of open rates is being too generic. Subject lines like "App Update Available" or "Newsletter #47" tell your users absolutely nothing about what's inside. Your mobile app users get dozens of emails every day—they need a compelling reason to open yours instead of deleting it straight away.

Writing Subject Lines That Sound Like Spam

Using ALL CAPS, excessive exclamation marks, or words like "FREE!!!" might seem attention-grabbing, but they actually work against you. Email providers flag these as potential spam, which means your carefully crafted message might never reach your users' inboxes. Keep it natural and conversational.

Forgetting About Mobile Screens

Most people check their email on mobile devices, yet so many app developers write subject lines that get cut off after 30 characters. If your subject line is "Your Weekly App Performance Analytics Report Is Ready", users will only see "Your Weekly App Performance..." That's not going to inspire anyone to tap open.

The best subject lines for mobile apps focus on the user's benefit, not the app's features

Another common mistake is sending emails at the wrong time. Just because you finished writing your email at 2am doesn't mean you should send it then. Your users are probably asleep! Schedule your emails for when people actually check their phones—typically mid-morning or early evening work well for most mobile app audiences.

Crafting Subject Lines That Work on Mobile Devices

Mobile screens are small—really small when you think about it. Most email apps only show about 30-40 characters of your subject line before cutting it off with those annoying three dots. This completely changes how you need to write your subject lines compared to desktop email marketing.

I've learnt this the hard way over the years. You can't just take a desktop subject line and expect it to work on mobile. The front-loading principle becomes absolutely critical here—you need to put your most important words at the very beginning of your subject line. If your app sends workout reminders, "Workout reminder: 15-minute HIIT session ready" works much better than "Get ready for an amazing 15-minute HIIT workout session today".

Mobile-Specific Best Practices

Keep your subject lines between 25-35 characters when possible. Use numbers and symbols strategically—they stand out more on small screens. Emojis can work brilliantly here too, but don't overdo it. One well-placed emoji can make your email pop in a crowded inbox.

Preview text becomes your secret weapon on mobile devices. This is the snippet that appears underneath or next to your subject line. Most people ignore this, but it's prime real estate for mobile users. Use it to extend your message or add context that didn't fit in your subject line.

• Test how your subject lines look on different mobile email clients
• Avoid starting with words like "Re:" or "FWD:" as they waste precious character space
• Use action words early in the subject line
• Consider how your subject line works with your sender name

The mobile inbox is a harsh environment. Your subject line has maybe half a second to grab someone's attention before they scroll past. Make every character count.

Testing and Measuring Your Subject Line Success

Right, so you've crafted what you think is the perfect subject line for your mobile app's email marketing campaign. But here's the thing—you won't actually know if it works until you test it properly. Testing subject lines isn't just about sending one email and hoping for the best; it's about using real data to understand what makes your app users tick.

The most straightforward way to test subject lines is through A/B testing (sometimes called split testing). You send two different subject lines to small portions of your email list—maybe 20% gets version A and 20% gets version B. After a few hours, you look at which one has better open rates and send that winning version to the remaining 60% of your list.

What Numbers Actually Matter

Open rates are your primary metric here, but don't ignore click-through rates either. A subject line might get people to open your email, but if they're not engaging with your app afterwards, something's not quite right. Most mobile app email marketing campaigns see open rates between 15-25%, though this varies massively depending on your industry and audience.

Making Testing Work for You

Test one element at a time—if you change both the subject line length and the emoji usage, you won't know which change made the difference. Keep detailed records of what works and what doesn't. Your app users might respond differently to subject lines than other audiences, so build your own database of successful approaches.

Only test subject lines when you have enough subscribers to get meaningful results. If you're sending to fewer than 1,000 people, the data won't be reliable enough to make decisions from.

Remember, what works today might not work next month. User behaviour changes, especially in mobile app marketing, so keep testing regularly to stay ahead of the game.

Advanced Techniques for Different Types of App Emails

Here's the thing about app emails—they're not all the same. The subject line that works brilliantly for your welcome email will probably fall flat for a re-engagement campaign. After years of working with app developers, I've learnt that different email types need completely different approaches to their subject lines.

Let me break down the most effective techniques for each type of app email you'll be sending.

Welcome and Onboarding Emails

These emails should feel warm but not overly excited. Your new users just downloaded your app—they're already interested. Subject lines like "You're all set!" or "Ready to get started?" work well because they focus on what happens next rather than trying to sell something they've already bought into. Effective onboarding practices always consider the specific type of app and user expectations.

Push Notification Follow-ups and Feature Announcements

For these emails, curiosity works better than direct statements. Instead of "New feature available," try "Something new is waiting for you" or "We've been busy." The mystery makes people want to know more, and that's exactly what gets emails opened. When announcing updates, consider best practices for app update notifications to maintain user engagement.

Re-engagement emails need a completely different tone. These users haven't opened your app recently, so being pushy won't help. Subject lines that acknowledge the gap work well: "We miss you" or "It's been a while" feel personal without being demanding. The key is making them feel wanted, not guilty about being away.

Conclusion

Writing effective subject lines for your mobile app's email marketing isn't rocket science, but it does require some thought and planning. Throughout this guide, we've covered the psychology behind what makes people tap that email in their inbox, the technical bits like keeping things short for mobile screens, and how to test what actually works for your specific users.

The truth is, there's no magic formula that works for every mobile app out there. What gets your fitness app users excited might fall completely flat for people using your banking app—and that's perfectly normal. The key is understanding your own users and what motivates them to engage with your emails.

Remember to keep testing different approaches; what worked last month might not work next month as your user base grows and changes. Pay attention to your open rates, but don't obsess over them—a slightly lower open rate with more engaged users is often better than high open rates from people who immediately delete your emails.

Most importantly, always put yourself in your users' shoes. They're busy people with dozens of apps on their phones and hundreds of emails in their inbox. Your subject line needs to earn its place amongst all that noise by being clear, relevant, and genuinely useful. If you can nail that balance whilst staying true to your app's voice and purpose, you'll see those open rates climb naturally over time.