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Your customers' inboxes are inundated with marketing emails, Every. Single. Day.

That's why it's essential to hit your first touchpoint—the email subject line—out of the park.

To ensure your referral emails aren't heading straight to the trash, here:

  1. I explain the role well-written referral email subject lines play in referral marketing,
  2. I've fleshed out the most notable referral email subject line best practices,
  3. and I've put together a list of the 10 best email subject lines. 


Why Your Referral Program Email Subject Line Is Important 

As inconsequential as they may seem, the few words that make up an email subject line are the most important you'll write when creating emails for any promotion—referral emails included.

According to OptinMonster, 69 percent of email recipients claim they will report an email as spam based solely on its subject line.


Zippia reports that 64 percent of email recipients base their decision on whether to open an email entirely on a subject line. And, a third—33 percent—of email recipients open an email thanks to a catchy subject line.

Yup. Email subject lines may seem insignificant, but, as the stats show, not taking them seriously can have a significantly negative impact on your brand's referral program.


6 Features of a Good Referral Email Subject Line

Okay. So we now understand the importance of email subject lines, but what are the actual features of a good referral email subject line?

Let's parse this out now.


1. Be concise and specific

Ideally, a good subject line should be specific and to the point. It ought to give your recipients a brief overview of what they can expect from reading your email.

There are two key reasons for this:

1. Email platforms only preview a certain amount of characters.

Too long and an email subject line will be cut short and will hide part of the message from your readers. To put a number on it, email subject lines previewed on an iPhone are cut off after 41 characters (in portrait view). With 46 percent of emails opened on a mobile device, it's important to optimize a subject line's length with iPhones in mind. While in Gmail, that is extended to 70 characters when viewed on a desktop computer.

FYI: According to Litmus, Gmail is the most used email client, holding a 27.8 percent market share—Apple a fraction behind with 27.6 percent.

2. A tight, concise email subject line makes for easy reading.

Meaning a recipient is more likely to take the time to read it if it isn't drawn out and long-winded. For example, "Get $10 off your next purchase when you refer-a-friend!" is okay, but it will be cut short when viewed on an iPhone and, at 55 characters, is longer than it needs to be. 

Comparatively, "Refer a friend, get $10 off!" conveys the same information, but it's only 31 characters long. So no matter which device a recipient is accessing this email, the subject line won't be cut short, and it's much easier to read.

This is particularly important when skim reading. Which, I'm confident in saying, we all do when sorting through the mass of emails that pile up in our inboxes.


4 words

5 words

6 words

7 words

8 words

9 words

10+ words

Open rate








Click-to-open rate









To really push this point home and give you some absolutely solid, no-fluff numbers, according to an analysis by Marketo, the best referral email subject lines have a length of four to seven words. Subject lines with four words receiving the highest open rate and subject lines with seven words receiving the highest CTRO (click-to-open rate, meaning the percentage of recipients who opened the email and proceeded to click a link within that email).


2. Use power words

As a great man once said...

Words are powerful things. They evoke an emotional response, influencing the way we think and feel. When you're choosing words for your email subject line, you need to be aware of this power. Choosing the right words will make recipients more likely to open and read an email. Conversely, the wrong word choice can turn people off reading your email, and even trigger spam filters.

Not the response to your referral emails that I'm sure you're hoping for.

To be sure you're writing engaging subject lines, use what's referred to as keywords or power words. Here are power words (and phrases) that evoke different emotional states:

  • 👍 Instill exclusivity - "confidential," "custom," "early access, "extraordinary," "invitation," "limited," "members only," "offer," "pre-sale," "secrets," "special sale," "under wraps."
  • 👍 Build trust - "according to," "backed," best-selling," cancel anytime," case study," certified," endorsed," fully refundable," "research," results," studies show," "tested."
  • 👍 Use flattery - "accomplishment," "admirable," "amazing," "awesome," "brilliant," "exceptional," "impressed," "perfect," "proud of," "remarkable," "smart," "terrific."
  • 👍 Exploit FOMO - "doorbuster," "don't miss out," "last chance," "limited discount," "limited-time," "one-time offer," "time's running out."
  • 👍 Solve pain points - "avoid," "beat," "easier," "faster," "hassle-free," "improve," "increase," "quickly," "save," "upgrade."

For comparison, here are some examples of the wrong choice of words and phrases that are often viewed as sales-y and gimmicky (these words and phrases are also known to flag spam filters):

  • ⛔ Words - "earn," "cheap," "free," "opportunity," "winner," "miracle," "guarantee," "million," and "click."
  • ⛔ Phrases - "your income," "be amazed," "earn $x per week," "call now," "act now," and "free trial."
  • ⛔ CAPSLOCK. This screams spam and, if it's not flagged by spam filters, it looks like you're SHOUTING at the recipient.
  • ⛔ Phrases like "Hey! I need your help!!!" We all know what this really means. You're about to ask for a favor. That means commitment. Nobody wants that. Plus, you're tempting fate with those excessive exclamation marks.
  • ⛔ "You won't believe what's happened!" This is too clickbait-y and vague. Be more specific in your subject line so that recipients know what they're getting themselves into before they open your email.
  • ⛔ $$$. Nope, don't do that either.


3. Personalize it

Consumers are becoming immune to mass marketing.

In the past, businesses would simply use email blasts to distribute marketing material to their entire email list. And while this technique still has its uses, in a sea of generic communications, email blasts aren't always the best approach for connecting with existing customers.

Sometimes personalized emails are the only way to catch your readers' eyes. Personalized emails are those that are addressed to a specific person, rather than to a general audience. A personalized email shows the recipient that you value their relationship and are willing to take the time to write a message that is specifically tailored to them. This may mean that the subject line aligns with a recipient's interests, needs, or past purchasing behavior.

So how do you make your referral emails feel personal and non-generic?

There are a couple of tactics you can employ, including:

  • Addressing the recipient by name. Campaign Monitor found that using a recipient's name as the first word of an email subject line increase open rates by close to 15 percent.
  • Offering tailor-made referral rewards. 91 percent of consumers claim they are more likely to do business with a brand who recognizes, remembers, and provides relevant offers.
  • Using personalized messaging. 71 percent of consumers expect personalization while 72 percent claim they will only engage with personalized messaging.
  • Speaking to different demographics. If, for instance, we look at age brackets, 70 percent of millennials find irrelevant, impersonal emails frustrating.


4. Use customer segmentation

Speaking of demographics and their preferences, customer segmentation is "muy importante" (very important) to the success of your referral emails. By segmenting customers based on factors such as past purchase history, geographical location, or, as we just discussed, their age, businesses can send targeted emails that have a greater likelihood of converting.

To give you an idea of just how important customer segmentation is to your business, consider this:

  • 77 percent of marketing return on investment (ROI) is derived from segmentation, targeted, and triggered campaigns.
  • Mailchimp saw a 14.3 percent higher open rate in segmented campaigns and a 101 percent higher click-through rate than in non-segmented campaigns.

As you can see, customer segmentation not only results in more conversions, but when customers feel like they are receiving personalized messages that are relevant to them, it also leads to a higher level of engagement.

Learn more about Friendbuy’s various customer segmentation features, including widget user segmentation.


5. Use emojis (wisely)

There's a slight difference in opinion when it comes to the use of emojis in email subject lines. 

Some analysis shows emojis decrease email open rates, while other analysis shows emojis boost open rates.

So what's the deal?

Well, according to MailerLite, it depends on which industry or niche your business resides within. For example, MailerLite's analysis found that telecommunication audiences aren't that keen on emojis—emails without emojis receiving 30.61 percent open rates and emails with receiving 19.14 percent open rates, a difference of -11.47 percent.

On the other hand, the higher education crowd quite enjoys the addition of emojis in email subject lines—emails without emojis saw 26.51 percent open rates and emails with got 32.98 percent open rates, a difference of +6.46 percent.


Average open rate without emojis in subject lines

Average open rate with emojis in subject lines

Impact on open rates

Health and Fitness




Education and Training












Media and Publishing








Marketing and Advertising




Educational institution












Business and Finance








Arts and Artists








Travel and Transportation




Online courses












Entertainment and Events




Beauty and Personal Care




Creative Services








Software and Web App




Medical, Dental, and Healthcare




Real Estate




Publishing company








Music and Musicians




Agriculture and Food Services




Computers and Electronics




Home and Garden












Photo and Video
















Architecture and Construction
















Recruitment and Staffing




Information Technology (IT)












Higher Education








Daily Deals/E-Coupons




Art gallery and museum




Table and data from MailerLite. If you’re interested in seeing more industry email marketing data, check out their 2022 Email Marketing Benchmarks.

Just another example of why customer segmentation is so important. By dividing a customer base into separate groups, you can target them with individualized and engaging subject lines that either do or do not contain emojis.

But how is this determined?

With A/B testing, of course.


6. Use A/B testing to find the best open rates

Without A/B testing, companies are basing their marketing decisions on guesses and hunches rather than solid data. A recipe for wasted resources and money.

How does A/B testing work?

In technical terms, A/B testing is a method of experimentation whereby two different groups are created, one as a control group and the other as a treatment group. Each group, or variant, is then presented to users at random.

In digital marketing, this might take the form of comparing the click-through rate (CTR) of two different email subject lines, or the conversion rate of two CTA button designs. By randomly assigning customers or visitors to one of two groups, and then exposing them to different versions of a product or service, marketers can measure which version performs better than the other.

How do you use A/B testing in referral marketing?

Well, tools like Friendbuy's platform have integrated A/B testing capabilities that allow you to create different versions of your referral marketing material and then track the results to see which one performs better—including email subject lines.

If you'd like to learn more, check out a detailed breakdown of Friendbuy's A/B testing features here.


Examples of Referral Email Subject Lines

You now know the importance of well-written referral email subject lines and the technical aspects behind what makes them successful, but how about putting this knowledge into practice?

To help you get started, here are some top-performing examples to pull inspiration from.

Oh, and FYI: we also have a comprehensive guide on refer-a-friend email templates. Don't miss it.


Referral program awareness

These are emails you send out as an email blast. They are typically sent to your entire email list and aren't segmented by recipients' buying preferences, age, or other demographic factors.



Subject line: "Invite friends to earn up to $150 👀"

ReadyFresh's latest referral program email marketing campaign is sure to get noticed. With an engaging subject line like "Invite friends to earn up to $150 👀," how could you not be intrigued?

$150 is no small amount.

This is a perfect example of something we continuously advocate for here at Friendbuy. If you have an irresistible referral incentive, show it off by including it in your referral email subject lines. Seriously, it's one of the best ways to boost open-rates.


Smile Direct Club

Subject line: "🦷 Hurry! Earn $100 before it's too late."

Same goes for Smile Direct Club's recent referral program email campaign. Before a recipient even opens the email, they know something exceptional awaits them—$100.

The word "hurry" establishes a feeling of urgency. They also threw in a tooth emoji to both spark interest and align with Smile Direct Club's branding and core message, dental health. And Smile Club Direct's offer to reward an Advocate's friends with $100 off their aligners will really seal the deal.


Outdoor Voices

Subject line: "Give and you shall receive... $20!"

If you're not signed up for Outdoor Voices' email list, you're missing out on some seriously engaging subject lines. With the latest email marketing campaign featuring the subject line "Give and you shall receive... $20!", the activewear brand's referral program encourages current customers to share their love of the company's products with Friends.

Once opened, the email goes on to describe the company's referral process and the benefits of its referral program, including a $20 discount for both the advocate and the friend. Outdoor Voices also included a prominently placed CTA button, allowing customers to access their unique referral link and begin spreading the word about their brand.


Referral contests, sweepstakes, and giveaways

A referral contest, sweepstakes, or giveaway are used to encourage participants to enter to win prizes by referring friends or family members to a company's products or services.

Sweepstakes are similar to contests, but the prize is usually given away randomly instead of being awarded to those who refer the most new customers. Giveaways are promotions where businesses give away products or services for free in order to generate interest in their brand.


Smile direct Club

Subject line: "Refer for a chance to win $500."

Smile Direct Club recently ran a referral contest where they offered customers a chance at winning $500—the more referrals, the more entries, and the greater the chance of winning. The subject line of the email was "Refer for a chance to win $500."

The kicker?

Even if the Advocate didn't win, they still received a $100 Amazon gift card for every new customer they referred.

The campaign was a success, with many customers taking to social media to share their unique referral link. Smile Direct Club saw a surge in new sign-ups and increased their customer base.

If you're looking for a way to increase your customer base, why not try a referral contest? It's a great way to incentivize your existing customers and attract new ones.


Limited-time offers

A limited-time referral program offer is just as it sounds. It is a promotional offer from a company that encourages customers to refer new customers or clients within a specific timeframe. This type of offer can be used to jumpstart word-of-mouth marketing and grow a customer base quickly.



Subject line: "Raise a glass to bourbon month 🥃"

To celebrate bourbon month, Flaviar, a fine spirits and whiskey subscription service, previously ran a limited-time referral email marketing campaign. The subject line of the email is "Raise a glass to bourbon month 🥃."

In the email, Flaviar explains that for every Friend who signs up for a subscription using the referral link, the Advocate will receive a bottle of bourbon. In return for signing up, the Friend also receives a bottle of bourbon.

This campaign was a great way for Flaviar to boost its subscriber base while also rewarding its existing customers.


Friend incentive

Friend (the referred) incentives are sent to recipients after they have been nominated by an Advocate (the referrer). These types of email messages are targeted at new customers, offering attractive rewards to prospective customers that decide to take part in a company's referral program.


Dollar Shave Club

Subject line: "Congrats! [advocate’s name] has nominated you"

Dollar Shave Club's friend incentive referral emails demonstrate what incentivization is all about. The subject line of the email is "Congrats! [Advocate’s name] has nominated you." The body of the email explains that if Friends sign up for the service, for just $1 they'll receive their choice of razors, a reusable handle, and a cassette of replacement cartridges.

Included is also a CTA button that links the recipient to the referral program's landing page where people can sign up.

It is clear that Dollar Shave Club wants people to share their experience with their Friends. By offering (essentially) a free month of shaving, they are giving people an incentive to do so.



Subject line: "[Advocate’s name] is sending you 10% off at"

SPANX, the company that makes women's favorite body-shaping undergarments, is at it again. This time, they're encouraging their customers to spread the word about their products with a Friend incentive referral email marketing campaign.

Here's how it works: for every Friend the Advocate refers to SPANX who makes a purchase, they'll receive a 10% off to use on your next order.

To sweeten the deal even further, SPANX offers the friend the same incentive—10% off. So not only will you be able to save on your next purchase, but your friends will be able to get a great deal too.

Learn how SPANX uses Friendbuy to achieve a 15% conversion rate from referred customers.

Social Gifting

In referral marketing, social gifting is offering current customers the opportunity to give away a company's product or service to a Friend at no cost to either party.

This is a great way to reward Advocates or loyal customers, as it allows them to give something special to a friend or family member. For the recipient of the gift, it's a nice little surprise. And for companies, it's a surefire way to build goodwill and strengthen relationships with customers and potential customers.



Subject line: "Brighten someone's day on us."

Feals, a CBD company, have come up with a new way to get customers to spread the word about their range of products: social gifting.

Here's how it works: after a customer makes a purchase, they are presented with an opportunity to share a "free flight" with a Friend. To do so, they simply enter their own email and a Friend's email.

The Friend then receives an automated email from the Advocate, which includes a CTA button that links them to a landing page where they can claim their "free flight".

It's a simple enough concept, but there's one key element that makes Feals' social gifting campaign stand out: the subject line. Instead of something mundane like "Refer your friends and save," Feals' referral email subject line says "Brighten someone's day on us."

The perfect phrase to inspire a touch of altruism.


Loyal Advocates

Sometimes you just want to say thanks and make your most loyal customers feel extra special (and, of course, create another opportunity to promote your referral program). Because at the end of the day, everyone benefits from a strong referral program—the company, its customers, and its advocates.



Subject line: "You mean everything to us. Thank you ❤️"

With a witty subject line and a well-executed email campaign, Persona was able to get its email messages across to its VIPs and loyal Advocates.

To participate in the campaign, customers can simply refer a friend or family member to Persona through the company's website. For every successful referral, the customer will receive a $25 Amazon gift card and, in return for placing a $50 order, each Friend receives $20 off their next order.



A post-purchase referral email is an email that companies send to an Advocate after their Friend has carried out a specific action. These emails detail how the advocate can claim their originally proposed referral reward.



Subject line: "You just earned a $100 gift card 🥳"

After an Advocate's friend makes a purchase on Casper’s website, they receive a post-purchase email with the subject line, "You just earned a $100 gift card 🥳." In the email, Casper thanks the customer for their referral and explains how they can claim their $100 reward.

By sending this reward, Casper is not only thanking the Advocate for their past patronage but also incentivizing them to continue to do business with their company.

So if you're looking for some inspiration for your own post purchase referral email marketing campaign, take a cue from the example set here by Casper.

How Casper Generates Greater Return With Referral Marketing

For more effective ways to boost the performance of your referral program, see our referral program examples here



There's no magic formula that'll see your referral email marketing reach success. But, as a reminder, if you follow these simple rules when crafting referral email subject lines:

  1. keep it clear and specific,
  2. stand out with power words,
  3. make it personal,
  4. segment your audience,
  5. use emojis in the right context,
  6. and A/B test

you will no doubt find success.

If you feel your business could benefit from referral programs, then reach out to us here at Friendbuy.

Friendbuy is an online-based platform built to help businesses, like yours, increase their customer base through referrals. Our platform provides businesses with a customizable referral program that they can use to track referrals, pay out rewards, and monitor results.

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