Email subject lines can be your foot in the door or your foot in the mouth. It all comes down to the words that you choose, the length, the value…

…The truth is, your subject line’s effectiveness comes down to a lot of factors for such a small word count.

The best email subject lines should check all of these boxes:

  • Be between 1-5 words in length
  • Summarize the intention of your email body
  • Tie nicely with the first line of your email body
  • Reflect type of email (initial, reply, forward, or follow up) (i.e. “re,” “fwd,” “next steps”)
  • Get the attention of recipients who are strangers and “pop” when they scan their inbox

Their function in an email is very important:

Below are tips and tactics for writing email subject lines that get opened to lay the red carpet for emails that get replied to.

The key here is that the advice below is backed by data. We’ve analyzed 115,000,000 million emails sent by 7,839 different companies to give you the most important takeaways.

That’s a lot of emails.

When you look at an aggregate this large, the beauty is that what others might observe as a trend becomes a hard reality with millions of email opens (or lack of opens) behind it.

You’ll learn:

  • The right length for your subject line
  • Sabotaging phrases you’re absolutely forbidden to use
  • The best time to schedule your email
  • How the best email subject lines are formatted
  • 85 spam triggers that will trap your email in filters
  • 5 final ideas on how to crush your subject line


The Right Length for Your Subject Line

Open Rates Peak Between 1-5 Words.

The most successful emails based on open and reply rates had subject lines between 1-5 words. This supports our common belief that clear and concise is key to generating the perfect subject line. Your subject line should describe the contents of the message concisely but remain short enough for your recipient to read it on their phone. Always keep mobile users in mind and never exceed 7 words in your subject line.

You’re Absolutely Forbidden To Use These Sabotaging Phrases

Did you know for every 100 emails sent with the subject line “Can you chat?,” less than 2 get replied to, and under 1 in 10 people reply to emails that ask “something of interest?”

Do try these techniques:

Include numbers — i.e. 33% More SQLs. (Wins 53.2% vs 51.9% average for opens and 32% vs 29.8% average for replies.)

Mention customer name that your recipient likely knows and respects (i.e. “How Lyft 3x-ed Closed-Won.”)

Get creative — find an interest of theirs and connect it to what you’re writing about. I.e. “Surf’s up” (the opening of email uses metaphor to tie surfing to your intention. Example here.)

Try sending a blank subject line (our analysis of 115M tracked emails shows that it has won >60% opens and >40% replies for our users, but see if it ultimately increases replies for you.)

Stay away from these:

Assuming things based on your own needs (i.e. that they want to connect too — it’s mutual, right? You just need to find the right time. Wrong.)

Asking a question and expecting a response when you haven’t won their trust yet. The open rate for subject lines posted as questions: 41.6%, reply: 18.4% (that’s a 10% drop in opens and an 11% drop in replies)

Using exclamation points — it lowers opens by 22% and replies by 25%                                                           

Using a personal greeting — lowers opens by almost 4% and replies by 8%. Why: it’s an early warning of a sales email.

Stating that your request or question is quick (because you and they both know it isn’t).

The Best Time to Schedule Your Email: How Time & Urgency Improve Reply Rates

What’s the intention of your email?

This will dictate your best send time.

Cold emails should be sent when there’s the least amount of competition. (we’ve found that open and reply rates are highest when you’d least suspect: on the weekends, and generally at 7AM and 8PM local time).

Post-meeting follow-up emails should be sent same-day if you’ve just had a meeting.

No-reply follow-up emails should go out the next day for an immediate need or a couple days out if your goal is slower nurture. You can automate an entire drip campaign right from your inbox to set up follow-up emails to send on their own if they don’t reply.

How the Best Email Subject Lines Are Formatted

The ultimate dilemma: Title Case, Sentence case, or lowercase?

Most outgoing emails are sent in Sentence case (53.17% of outgoing emails). That said, research shows that Title Case May Be The Way To Go:

Remember: Test for yourself. Use a feature like Templates that lets you A/B test the same email body with a different subject line.

85 Spam Triggers That Will Trap Your Email in Filters

One in four American business emails are either marked as spam or go missing.

The words you choose in your subject line might be preventing you from reaching your prospect in the first place.

Here are some words that you should avoid in your subject line to play it safe:




Other subject line triggers are ALL CAPS and exclamation points. Cut them outta there. ✂

5 Final Ideas on How to Crush Your Subject Line

Two fundamentals to never forget: 1) know your readers, and 2) deliver value. Here are tactics that use these elements to get them to bite:

1. Give relevant resources

You need to give in order to get.

It’s all about the rule of reciprocity. We feel obligated to repay to others what they provide to us.

Which means when you give someone a resource that helps them in their day-to-day job, they become more likely to agree to the conversation you’re starting.

It’s the same reason we say thank you when someone holds the door.


How to A/B Test Emails
8 Tips from Peers

2. Compliment the recipient

Words that praise are magic.

Even when we know someone has an ulterior motive behind complimenting us, their words still have the same effect. They make us think more positively of the person who offers them.

This is pretty remarkable.

Our minds can flag insincerity, but our emotions can’t discern it. Use this to your advantage.


Awesome news re: expansion 🎉
You did it 🎈

3. Rub a pain point

When we relate to something, it activates a part of the brain called the insula (our emotional powerhouse). And we all know emotion drives us to react (read: open).

So your job is to address their pain point in the subject line to get an open, and then solve it for them in the body of your email; this will be what drives the reply.


Too much in a day?

4. Step outside the box

Just make sure the body of your email doesn’t take a 180° turn from your subject line. You need clickbait, but make the bait relate (that’s a rhyme to help you remember).


Why’d you do that?

[BONUS: What are your best subject lines? Stop guessing, start tracking.]

5. Try these tools to help you send smarter emails

So, now you know which subject lines to use, avoid, and craft on your own. But you can take it a step further.

Ready to keep optimizing?

10 Cold Email Formulas That Just Plain Work

Examples of cold emails that are proven to work, with explanations backed by behavioral science. Have this PDF by your side as you write.


Email Subject Lines That Actually Work

Take it from our data scientists — and the 115 million emails they analyzed — exactly what you should and shouldn’t write in your next email subject line.


The 7-Day Crash Course in Sales Prospecting

The average person’s attention span is 8 seconds. Which is why we have this bite-sized email course for outbound salespeople.

Join our community of 800,000
empowered sales professionals

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