Planning to use email to grow your customer base and revenue?

You need to share the right messaging with the right people in the right formats-and one of the best ways to do that is optimizing your campaigns by A/B testing.

Continuously A/B testing your email campaigns not only makes your marketing team more capable of adapting quickly to changing preferences, but also gives you greater insight into what makes your recipients engage with your emails. And when you know what's working and what's not, your email marketing efforts are more likely to make money for your business.

As we dive in to 11 email campaign optimization best practices, keep these general A/B testing rules in mind:

1. Optimize subject lines for urgency and context

Subject lines are arguably the most important copy element you'll write for your email marketing campaigns. When you A/B test your email subject lines, you can increase your open rates in a cost-effective way.

(Apple's 2021 privacy changes impacted the reliability of using open rates as a benchmark-meaning your open rates might seem high, but only because Apple's own process counts as an open. But your email open rate can still be a directionally helpful metric, as long as you're tracking it in conjunction with other metrics and not over-relying on it to tell the story of your email performance.)

Here are a few ideas for A/B testing your subject lines:

• Length: Compare shorter subject lines (<50 characters) with longer ones (50-70 characters) to find out which performs better with your audience.
• Preview text: Play with the length and tone in this "teaser" to your email content, but always make sure it complements your subject line. Determine how this impacts open rates.
• Urgency and scarcity: Try different words and phrases that inspire readers to take immediate action. Monitor your results.
• Emojis: Test emojis in subject lines to add visual appeal and convey personality. Analyze whether emojis improve open rates.

Klaviyo AI can help you develop subject lines at scale. Test AI-generated subject lines against one another to determine which ones yield better results at a higher volume. Klaviyo's smart A/B testing also makes it easy to see which email subject lines perform the best, then automatically serves up the winner to the majority of your recipients for any given campaign.

2. Test incentives carefully to drive interest

It's common to add a discount to your email campaigns to drive conversions. But a lot of brands (rightfully) hesitate to do so, because they're worried about value perception and profits.

Higher discounts don't always lead to higher conversions. Klaviyo's 2023 Black Friday Cyber Monday data shows that the 3 most common discounts during that time period were 30%, 20%, and 25%, in that order. Data also shows that discounts in the 20-29% range converted best across all industries.

Moral of the story: customers have brand preferences, and "deals" aren't always powerful enough to sway them. But A/B testing can help you work out these considerations. In addition to testing discount amount, you can also test incentive type:

• Percentage off
• Dollar amount off
• Free gift with purchase
• Chance to win a contest or giveaway
• Free shipping
• PDF downloads and guidebooks

Clothing brand Brava Fabrics, for example, used to offer a 10% discount when people subscribed. Then they A/B tested it against the chance to win €300 worth of products-and found that the two offers performed the same. Offering one customer a prize rather than a bulk discount was just as effective and protected the brand's marketing budget.

3. Take advantage of seasonal engagement

Brands often align their email campaigns with the biggest holidays and ecommerce events to drive seasonal engagement and conversions. Seasonal and holiday email campaigns are great for strategic planning, and they make it easy to maintain consistency and take advantage of cultural timing.

Like apparel brand Jenni Kayne in the email above, here are a few ways you can test and optimize your seasonal and holiday campaign messaging:

• Holiday-themed copy: There are only so many ways you can wish someone season's greetings, so get creative with your copywriting. Play around with holiday phrases and connect your offerings to the season. For example, you could try "ringing in" savings for a New Year's sale, or asking subscribers to not "ghost" you during Halloween.
• On-brand visuals: Test different layouts and imagery to see what resonates most with your recipients-but make sure to stay on brand. Notice how Jenni Kayne's email design doesn't use sunbursts or "beachy" elements to promote their seasonal summer guide-instead, the design aligns with their minimalist, contemporary brand identity.
• Seasonal offers: Test different discounts, deals, and brand offers that align with the holidays. Jenni Kayne probably wouldn't push their fisherman's sweaters in summer, but they could create a July email campaign around sandals and accessories.

4. Drive clicks with punchy calls to action (CTAs)

The consensus on CTAs is they should be short and punchy-but what should they say? Is "Buy Now" too pushy? Is "Learn More" too vague?

The only way to find out what works for your brand is to A/B test your CTAs. A/B testing will help you craft CTAs that inspire action. Here are a few ideas for effective CTA testing:

• Number of CTAs: Test whether a single CTA vs. multiple CTAs drives more engagement.
• Placement: Experiment with the position of your CTA within the email. Does placing it at the beginning, middle, or end yield better results?
• Copy: Try different wording for your CTAs. Compare direct commands like "Buy Now" with softer suggestions like "Learn More."
• Color: Test various colors for your CTA buttons. A vibrant color might attract more attention, but it's essential to ensure the color aligns with your brand's color scheme.
• Buttons vs. hyperlinks: Assess whether your audience responds better to clickable buttons or text-based hyperlinks.

5. Design emails for maximum conversions

Create variations of your emails with different colors, layouts, copy, and images, and send these test designs to your selected email segments to determine which performs best.

Here are a few ideas for A/B testing email design:

• Different layouts or images: See which layout or image performs best with your audience.
• Copy- vs. image-heavy: Some people will engage more with text, while others prefer visuals.
• Conversion asset stacking: Give people a choice about how they move forward in their buyer journey. Each element should inspire recipients to take the next step. Your headline should lead to the subhead; the subhead should lead people to the CTA, etc.

6. Use AI to segment your audience more effectively

This one doesn't involve A/B testing, but it does involve email campaign optimization. Personalization is one ingredient in the secret sauce for generating higher engagement and conversions with your email marketing, and segmentation is the first step in the personalization equation.

When you segment your audience based on the data you've collected about them rather than batch and blasting generic marketing messages to everyone, your email campaigns are more likely to drive engagement and revenue-and AI can help.

AI segmentation tools like Klaviyo Segments AI create highly accurate and targeted audience segments in seconds after you type in a description of the people you want to reach-saving you time and enhancing your messaging's precision.

Predictive analytics, meanwhile, uses AI to anticipate your customers' needs and helps you forecast your audience's future actions and trends by analyzing historical data. With insights into buying patterns, customer lifetime value (CLV), and churn probability, you can use data to segment your audience more strategically.

Klaviyo will apply a combination of data science and machine learning to analyze predictions against your customers' information to generate useful insights:

• Historic CLV: total value of orders a customer has made
• Predicted CLV: prediction of how much a customer will spend within the year
• Total CLV: the sum of "historic" and "predicted" CLV
• Churn risk prediction: probability of a customer churning based on the number and frequency of orders
• Average time between orders: average number of days between customer orders
• Predicted gender: using a customer's first name along with census data to determine if a customer is likely female, male, or uncertain

The Willow Tree Boutique, for example, uses predictive analytics to promote luxury items to customers with proven spending power-a predicted CLV over $500, or an AOV over $150. Within the first 6 months of using Klaviyo predictive analytics, the team saw a 53.1% HoH growth in revenue for H2 2023.

7. Personalize further with product feeds and AI

In addition to segmentation, personalization methods like product feeds and AI-driven product recommendations help you tailor your email content so it resonates with each customer.

Product feeds pull together your product catalog and customer behavior data to curate custom product recommendations for each email recipient. Product feeds can integrate with your email campaigns to add another level of personalization to customer communications.

Recommendation algorithms use AI to dive deeper into customer data, analyzing your audience's past purchases and viewed products. AI recommendations help you predict what your customers will love next, and make it easy to deliver hyper-relevant product suggestions as part of your personalization efforts.

And this campaign optimization best practice pays off. During BFCM 2023, messages sent through Klaviyo that were personalized with dynamic content earned 17% higher average click rates and 40% higher average order conversion rates than non-personalized messages.

8. Achieve 1:1 personalization with advanced A/B testing

A/B testing is valuable because it teaches you what type of content resonates with the majority of your audience. But what about the section of your audience that actually preferred the losing variation?

With Klaviyo's personalized campaigns AI, you can A/B test emails at a never-before-seen scale.

This advanced A/B test process uses AI to search for patterns within groups of test recipients who engage with each email variation. After the testing period, Klaviyo will predict which variation performs better for each recipient and automatically send the rest of the segment this preferred variation.

That means instead of sending one campaign to everyone just because it performed best with the majority of recipients, you're sending the campaign most likely to resonate with each individual person.

9. Mind customer schedules and be smart about send times

The timing of your emails can make or break your campaign. Sending emails at the right time gets your messages into inboxes when your audience is most likely to open, read, and take action.

According to our research, the best days to send emails are Wednesday and Thursday. Across industries, average click rates and placed order rates tend to be higher on these days. But if you really want to drill down into the best timing for your email campaigns (hint: you do), A/B test different send times within those days to pinpoint your brand's sweet spots.

Here are a few ways to do it:

• Think about your readers' daily activities: Test email times when people are most likely to use or think about a product or service. For example, if you sell bedding or pajamas, test your emails in the evening. If you sell coffee, test your emails first thing in the morning.
• Consider seasonal schedules: For parents especially, schedules during the school year and the summer can differ significantly. Test for seasonal timing and your audience's daily responsibilities during different months.
• Take action by audience segment: Different audience segments will respond to different timing. For example, a working professional may respond better during their lunch break vs. a college student who may prefer checking email in the evening.
• Lean on AI: Your marketing platform should make it easy for you to A/B test email timing by splitting your audience into groups and sending emails at different times. If your list consists of at least 12,000 subscribers, Klaviyo's Smart Send Time can use your data to determine the optimal local time to send emails to customers.

10. Don't forget email compliance and unsubscribe links

It's important to keep your emails compliant with regulations like the CAN-SPAM Act, the General Data Protection Regulation, and Canada's Anti-Spam Legislation to maintain recipient trust and avoid legal issues.

Although this isn't an element you'll want to "test," you can test how you choose to present compliance information.

At a bare minimum, you need to include an unsubscribe link in your emails. Make sure you communicate transparently with your audience so they're aware of the frequency of your email messaging (and can opt out easily if they choose to). Monitor feedback and pay attention to responses and opt-out rates so you can tweak your strategy to engage your audience more effectively.

When you're monitoring this feedback, try testing different copy variations that may inspire your audience to reconsider before unsubscribing. Or, in other cases, you may want to test copy that reassures your audience it's okay to unsubscribe and you'll welcome them back at any time.

When it comes to email compliance and unsubscribe links, make them visible, keep them simple, and respect user preferences-which means promptly removing unsubscribed recipients from email lists. This helps you create a more trustworthy relationship with your audience and keeps you on the right side of the law.

11. Track and monitor performance to adjust campaigns quickly

Monitoring email campaign performance is essential for optimizing your approach and achieving the best results. Key metrics to track include:

• Deliverability rates
• Unsubscribe rates
• Click rates
• Conversion rates
• Email list growth
• Revenue per recipient

Klaviyo's 2024 benchmark report shows that the top-performing 10% of businesses drive 8x more revenue per recipient and convert 5x more subscribers than the average.

Want that to be you? Implement an ongoing A/B testing and campaign optimization strategy, and track your metrics so you can adjust what's not working-and lean in to what is.

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• How to get A/B testing right: nail the basics, then put optimization on autopilot
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• Legal Sea Foods drives $21K+ in Father's Day Klaviyo revenue with segmented testing