The Do’s and Don’ts of Email Subject Line Capitalization

You know that moment when you get an email screaming, “READ THIS NOW!” and you roll your eyes so hard you can see your brain? That, my friend, is the dark side of subject line capitalization.

In simple terms, subject line capitalization is how you style your email’s subject line letters lowercase, Title Case, or even UPPERCASE. And believe it or not, this tiny detail can make or break your email open rates.

So, if you're sending emails that end up in the “ignore” pile, maybe it's time to revisit your email best practices starting with how you capitalize.

Why Subject Line Capitalization Is More Important?

Research shows 47% of people decide whether to open an email based on the subject line alone. And that includes whether your subject line capitalization looks polished or is it like just texted at 2 AM after three espressos.

Real Life Example:

Imagine two subject lines:

• exclusive offer just for you

• Exclusive Offer Just for You

Which one feels more professional? Exactly.

The Do’s of Email Subject Line Capitalization 

1. Do Use Title Case for Formal Emails

Title Case (Capitalizing the First Letter of Every Major Word) gives your emails a polished, credible look. Especially when you’re sending professional newsletters, announcements, or B2B outreach, this style follows the gold-standard email best practices.

Example:

✅ Your Exclusive Invite to Our VIP Event

2. Do A/B Testing to Find What Works for Your Audience

What if your audience loves casual emails? Enter A/B testing. Try two versions of the same subject line one in Title Case and one in sentence case and see which gets more opens. That’s email best practices 101.

Pro Tip: Run A/B testing regularly because trends change faster than you can say "open rate."

3. Do Keep It Consistent with Your Brand Voice

If your brand is fun and casual (think BuzzFeed), sentence cases might feel more authentic. But if you’re a law firm or a financial institution, formal subject line capitalization keeps things serious and trustworthy.

The Don’ts of Email Subject Line Capitalization 

1. Don’t Use ALL CAPS Unless You Really, Really Mean It

Using all caps in your subject line capitalization is like shouting in someone’s face. Annoying, right? It can also trigger spam filters. If you have to use all caps, limit it to one or two words for emphasis.

Bad Example:

🚫 OPEN THIS EMAIL NOW!

Better:

✅ Final Hours: SALE Ends Tonight!

2. Don’t Forget A/B Testing Before Committing

You wouldn’t buy a car without test driving it, so why send an email without testing its subject line capitalization? A/B testing helps you discover whether sentence case or Title Case resonates with your subscribers. It’s not optional, it's one of the key email best practices.

3. Don’t Be Inconsistent 

One week you’re using Title Case, the next you’re screaming in ALL CAPS, and then you slip into lowercase minimalism. Your audience needs to recognize you instantly, and inconsistent subject line capitalization just confuses them.

What Experts Say About Subject Line Capitalization

Ann Handley, author of Everybody Writes, advises, “Be specific, be generous, and be human.” That applies to subject line capitalization too. Whether you use Title Case or sentence case, the goal is clarity and connection.

Marketing guru Neil Patel suggests that A/B testing isn’t just for fun data from these tests is one of the best ways to improve your email best practices, including capitalization style.

Conclusion

To cap it off, subject line capitalization might seem small, but it’s mighty. Stick to email best practices like being consistent, knowing your brand, and—most importantly—doing A/B testing. Your open rates will thank you.

Ultimately, there isn't a one-size-fits-all solution. Some audiences love casual sentence cases, while others expect professional Title Case. That’s where A/B testing works its magic. Test, learn, and tweak your subject line capitalization strategy.

FAQ

What exactly is subject line capitalization?

Great question! Subject line capitalization is how you style the words in your email subject lines whether you go with Title Case, sentence case, or ALL CAPS. It’s a small tweak with a big impact on open rates and falls under smart email best practices.

Why does subject line capitalization affect email performance?

Because first impressions matter! Proper subject line capitalization shows professionalism and follows email best practices, making your emails more likely to be opened.

Should I use Title Case or sentence case in my subject lines?

There’s no universal rule. Use A/B testing to see which style your audience prefers. Both can follow email best practices when used strategically.

Is A/B testing necessary for subject line capitalization?

Absolutely! A/B testing helps you understand which subject line capitalization drives better open rates. It’s a crucial part of email best practices.

Can using all caps in subject lines hurt my emails?

Yes. Excessive caps in subject line capitalization can trigger spam filters. Use them sparingly and always follow email best practices, supported by A/B testing insights.