Marketing / Email Marketing

The Ultimate Guide to Email Subject Lines

Nicole Gilotti

Updated: Jun 14, 2023 · 15 min read

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good email subject lines

Staying in touch with your leads is a critical part of your sales and marketing process. Where too many businesses fail, is treating emails like a chore, or worse yet, treating email subject lines as an afterthought.

Emails are the most common form of communication between most businesses and their clients, with an estimated 306 billion emails sent and received every day in 2020. Unfortunately, most businesses overlook the impact a good email subject line can have on sales and growth. If clients get irritated by your emails, they stop opening them. No open emails, mean no promos getting through, no product updates being seen, and no repeat business.

Don’t worry though, Keap has got you covered with tips on how to increase open rates and engagement from your email marketing and communication. After reading this post, you’ll have everything you need to strategically tailor your email subject lines and see better results than ever.

Jump ahead or keep reading:

Make sure you finish the entire article before you get started, we’ll cover the DOs, DON’Ts, of subject lines as well as the level of impact you can expect, so you can customize your tactics to suit your unique business.

Why Does Your Subject Line Matter?

Over 47% of subscribers open an email based on the subject line alone
Over 69% of subscribers mark an email as spam based on the subject line alone

Did you know that nearly 50% (yes, that’s half) of all email recipients, open the email based solely on the strength of a good email subject line? They don’t know for sure what the email contains, they don’t know how long the email will be, and they don’t know what benefit they’ll receive. An email is a mystery box until we add the subject line.

Have you ever seen Raiders of the Lost Ark?

We’ll try to avoid spoilers. At the end of the film, a very important artifact is placed in a boring wooden crate and stored in a warehouse. The only thing to identify this priceless, world-shifting discovery, is a serial number, as it sits, doomed to be forgotten amongst thousands of identical wooden crates. Your emails are priceless artifacts for your business, don’t hide them in a boring wooden crate.

It’s up to you to give your clients a reason to open your emails, among the hundreds of emails they get every single day.

Emails are constantly rolling in, no matter who you are. This means your subject line (and the window to attract attention) is being pushed further and further down the page with every shipping notification, birthday reminder, and sustainable sneaker ad that enters the client’s inbox.

By using proven, email subject line best practices, savvy entrepreneurs (of all industries) increase their open rates and increase repeat sales.

Some are DOs, some are DON’Ts. By the time you’re done with this article, you’ll know the difference.

Tried and True Email Subject Line Best Practices and Tactics

Piquing Curiosity and Starting a Conversation in Your Email Subject Lines

If you want attention, you need to be interesting. This one seems pretty obvious until you look at your own inbox. Look over the subject lines in your personal inbox right now. How many subject lines, actually grab your attention, and how many seem like something you’re already planning to delete? I’ll bet the closer you look, the more mediocre than good email subject lines you notice, you might even unsubscribe from a few. That—is the exact same reaction your subscribers have when you send emails with boring subject lines.

Curiosity is one of the most effective ways to entice subscribers because it doesn’t matter if you have something new or exciting to offer. All that matters is if you know how to start a conversation. What does that mean?

Imagine someone sees you on the street; they shout “HEY! I left something in your mailbox! OPEN IT!”. Most people not only aren’t going to open the mailbox, but some might even call the police. Instead, if that person said, “Did you see what came in the mail today? It was pretty amazing.” This is an open-ended question. The person begins to wonder, “What’s in my mailbox? Why is it so amazing? Is this something I ordered?”. By piquing curiosity, you create a question loop in their mind that can only be resolved by opening the mailbox (or email).

  • Have you ever seen a turtle dance?
  • You’ve been Invited.
  • The feature you’ve been asking for has arrived.
  • This will be our little secret.
  • Please don’t read this email
  • The 3 things missing from your marketing strategy.

Split testing is a great tactic to try if you’re not sure which subject line your readers will feel more curious about and click on.

Specialist email marketing consultant Jordie van Rijn conducted a subject line test and posted about it on his blog, The test compared open rates for a newsletter subject line that started with 1) “I promised to get back to you…” (relationship between sender and reader) and 2) “Your marketing briefing...” (discussing something belonging to the reader). Both inspired curiosity without revealing too much about the email contents. The result was that the relational subject line starting with “I” got over 7% more opens.

Retargeting Email Subject Lines

Retargeting is one of those strategies every entrepreneur wishes they’d implemented sooner. When we talk to business owners, they lament constantly about the sales and repeat business they’ve lost by not being aware of how easy, and powerful a simple retargeting strategy can be.

Some examples of high converting subject lines for retargeting campaigns:

  • Forget something?
  • One more thing…
  • Something from your wishlist just went on sale
  • Here’s that reminder you asked for…
  • Your favorite items are now 20% off!

Email Subject Line Personalization

People (even the most humble ones) love their own names. It makes them feel seen and important. Keap users will often make use of powerful merge fields here to easily deliver a personalized experience. By adding a subscriber’s name to your subject line, you not only drastically increase open rates, but you put the notion in the lead’s mind that you’re speaking directly to them. This is the sort of thing that makes you stand out in a flooded inbox.

  • Stephanie, here’s our latest article about corgis!
  • Brandon, download these animation tools.
  • Nicole, have you seen our latest font options?

Keywords to Get the Best Email Subject Lines

Sometimes your subject lines get a boost from clever writing and sometimes it’s best to simply follow the crowd. Just like SEO for your landing pages, choosing the right keywords (in this case the ones seeing the highest open response) is about keeping up on trends and following the numbers. With that in mind, here are the top 15 subject line keywords from high converting email subject lines for 2020 and 2021 (based on an analysis of 2.2 billion emails).

  • Upgrade
  • congratulations
  • revision
  • forecast
  • snapshot
  • monthly
  • deduction
  • Free / Free delivery
  • available
  • new
  • alert
  • news
  • update
  • Thanks

Emojis Make for Good Email Subject Lines

Many entrepreneurs and businesses are resistant to use emojis because they’re perceived as being childish or unprofessional. The fact is emojis are not only becoming a greater part of typical communication, but they can be a HUGE boost to open rates when used properly. Think of emojis like salt in a dish, add just a little and it elevates everything, but too much and your guests will be running for the exits.

The top 3 emojis for increased open rates:

  • 🙂
  • ❤️

As it turns out, emoji placement also affects recipients’ perception of a subject line.

Shelley Walsch, founder of content marketing agency ShellShock, tested 3.9 million emails. She found that 7 out of 12 analyzed campaigns indicated that including an emoji at the end of a subject line resulted in a better open rate than when the emoji is at the beginning.

Deadlines, Scarcity, and Fear of Missing Out (FOMO)

People hate missing an opportunity. Think about when you were a kid and you heard the bells of the ice cream truck blocks away. You’d start asking all sorts of questions; where is it? How far away? Will it drive down our street? By the time you ran outside, money in hand, you were primed to buy. No matter how old we get, we’re still triggered by the idea that something great is about to happen and we’ll be left out!

Set the notion of a ticking clock or limited quantities. You should help the client arrive at their eventual conclusion. When clients are busy they’ll let the opportunities you offer sit on the backburner, that’s why they need a motivator to decide.

FOMO driven email subject line examples:

  • Register by August 2nd!
  • I grew sales by 800% with…
  • For our first 500 sign-ups…
  • Only 6 hours left to sign up.
  • We just restocked.
  • This will not be replaying this event.
  • After this Friday, it goes into the vault.
  • Oops, looks like you forgot something.
  • You’re losing 15% of your sales, here’s why.
  • The 5 tips all marketers overlook.

3 tips on being commanding in your email subject lines

Clients and leads occasionally need a shove in the right direction. Entrepreneurs are beset with choices to make, one after another, minute to minute. Sometimes, they’re just looking to be TOLD exactly what they need. Provide confidence in your message and direction, then follow that up with data that backs up your claims so that a potential client can pull the trigger and feel good about their decision. Make them trust that you know what they’re doing and have their best interest at heart.

  • Register by 3 pm.
  • You need this upgrade if you want to succeed in 2022.
  • Your emails are underperforming. Use these tips to grow.

Lead with the video in your email subject line

The vast majority of your leads simply prefer video to text. If they think the effort being asked of them is lower, it raises their likelihood to open your messaging. So if you have a video to watch in your email, let your leads know immediately. This is an excellent place to leverage your preview copy. Let your subject discuss the topic and you can inform them about the video with preview copy like:

  • Watch our video to learn more
  • August’s company update video is here
  • Everything you need to know in 90 seconds

Subject Lines to Avoid

The first few words that your email recipients see in their inbox can also inspire them to delete without even a click. So, what is it about your emails that’s sitting the wrong way?

Aaron Dinin, an entrepreneurship instructor at Duke who also holds an English PhD, dishes a bit of advice on what entrepreneurs should avoid when starting a cold email. One method to avoid is starting with a reminder that the recipient has already avoided you, such as “Just putting this message back at the top of your inbox.” Another is introducing yourself right out of the gate, which gives away immediately that the recipient doesn’t know you and should therefore avoid you.

Here are some other red flags to watch for in your subject lines.

Cut the SPAM Out

In 2021, over 45% of emails sent ended up flagged as spam.

This one may seem obvious, spam is bad. The problem is that most entrepreneurs have no idea they’re using words that frequently get flagged by service providers and email clients. What’s worse, if you end up in enough people’s spam folders (or the promotion tab in Gmail), your entire marketing machine can end up on a service provider black list.

Read next: How to Avoid Content Filters

Before you send out that next email marketing campaign, double-check your subject lines and make sure none of these terms are in attendance. This is where knowing what NOT to do should be part of your email subject line best practices.

Test your email spammyness and get a score before sending.

60 spam keywords to avoid in your subject line:

  • #1
  • 100%
  • $$$
  • Bargain
  • Beneficiary
  • Boost sales
  • Best price
  • Bonus
  • Bad credit
  • Cash
  • Consolidate
  • Call now
  • Credit
  • Clearance
  • Cures
  • Compare
  • Deal
  • Debt
  • Double
  • Earn
  • Eliminate
  • Extra
  • Financial freedom
  • Gift
  • Giveaway
  • Guaranteed
  • Investment
  • Income
  • Junk
  • Loans
  • Luxury
  • Lifetime
  • Money
  • Miracle
  • Money back
  • Multi-level marketing
  • No purchase necessary
  • No questions asked
  • Offer
  • Once in a lifetime
  • Order now
  • Passwords
  • Pennies
  • Prize
  • Promise
  • Profit
  • Risk-free
  • Rates
  • Refinance
  • Subject to…
  • Terms and conditions
  • Unlimited
  • Urgent
  • What are you waiting for?
  • While supplies last
  • Win/Winner/Winning
  • Warranty
  • Web traffic
  • Work from home

Keep Email Subject Lines ASAP: As Short As Possible

Your clients are busy, don’t waste their time. The subject line should give them a REASON to open the email. Save the details for the email itself. Keep it short, to the point, and never push the character count or your message will get cut off mid-...

Examples of short, effective subject lines:

  • It’s finally here!
  • Feature updates are available.
  • Join us tomorrow.
  • Half off everything in stock.
  • Sorry, you missed it.

Don’t Apologize

Your leads CHOSE to be on your list. As long as you’re sending them relevant content tied to their CRM info and behavior, they’ll never have a reason to be upset about an email from you. It’s only when businesses bombard leads with messaging, send random content, or repeat themselves that they see clients and leads hitting the “unsubscribe” button.

So as long as you’re acting in good faith and tailoring your content, there is no reason to apologize for communicating with your audience. You want what’s best for them, you have something of value to provide to them. But undercut their choice by making it seem as though you’ve lost confidence in your offerings. Because when you lose confidence, they lose confidence.

Some examples of subject lines to avoid:

  • Sorry to bother you.
  • Hope we didn't catch you at a bad time.
  • We know we’ve asked a lot, but…

Don’t Lie or Deceive

If you promise something, suggest something, or imply something—you need to deliver, otherwise, you’re just lying. Now there are marketers that will hide behind the idea that they didn’t “technically” deceive the client. If you want to create a brand and business that grows year after year, you need to build trust. Trust isn’t something you win, it’s something you cultivate constantly.

If you force your leads and clients to question the content you send them, they’ll not only lose trust for your brand, but they’ll see you as a chore to deal with, which will send them reaching for the unsubscribe button.

  • It’s impossibly simple; If you say it, do it. “$1 Million up for grabs!” —You better actually be giving away $1 Million.
  • “50% off everything in the store!”— If one item in your inventory isn’t 50% off, you lied.
  • “You just won…”—Either they won or they didn’t. Don’t use statements like this to drive sign-ups

Don’t guess, test!

Ensure any test is CLEAN, the objective is CLEAR, and the timeline is COMPLETE (3Cs).

Wrapping Things Up

We spend so much time cultivating the body of our marketing emails, we forget that the smallest piece of copy is the most powerful. Think of the average inbox as a grand library. There are hundreds, maybe thousands of volumes to choose from. If the title on the spine doesn’t shine, no one will ever read your story, no matter how epic.

Take your time, consider your audience and wherever you need to, refer back to these resources for high-converting, email subject line best practices:

  • Piquing curiosity and starting a conversation
  • Retargeting email subject lines
  • Email subject line personalization
  • Keywords to get the best email subject lines
  • Emojis make for good email subject lines
  • Deadlines, scarcity, and fear of missing out (FOMO)
  • 3 tips on being more commanding in your email subject lines
  • Lead with the video in your email subject line
  • Cut the SPAM out of your email subject lines
  • Keep email subject lines ASAP: As Short As Possible
  • Don’t apologize in your email subject lines
  • Don’t lie in your email subject lines

Looking to test these new subject lines yourself? See how Keap’s email marketing automation software helps entrepreneurs and small businesses simplify and automate email messaging.

Try a Free 14-Day Trial

About the Author

Nicole Gilotti is a Senior Email Marketing Manager at Keap. She has also managed email and direct mail for B2C companies like PetSmart, P.F. Chang’s and Caesar’s Entertainment. A self-proclaimed “email geek,” Nicole loves testing every aspect of emails (from subject lines to CTA button color) and dreaming up ways to personalize emails with dynamic content.

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