The Ultimate Guide to Email Optimization

How to Improve Email Campaign Performance

The world of email marketing, once a guaranteed messaging channel for a stagnant user base (cue dial-up noises here), is today a saturated collection of inboxes across multiple devices. In other words, it’s not about reaching everyone at a single device – it’s about making everyone feel like an individual person and reaching every device in the process! With this email campaign performance guide, we’re defining an email marketing strategy for how to target the right audience, deliver personalized and engaging content, improve email performance, and bolster all other marketing channels in the process.

Optimize Email For Your Audience

Businesses that actively tailor, or segment, their content to specific target audiences experience nearly twice the conversion rate of businesses with more generic approaches!

How Do You Use Segmentation in Email Marketing?

So, where do you start? First, look into your existing customer base. But remember, this isn’t just about finding a singular, ideal customer type. It’s about identifying which customer patterns exist in your sales funnel and how to communicate with these distinct patterns of customers in a hyper-personalized way — otherwise known as segmentation.

The segmentation process begins with collecting user data, most commonly through customer surveys and feedback forms, purchase history, website interactions, and social media engagement. This may include demographic data like age, gender, location, education level, income, or marital status. Customer preference data often includes product preferences, content types (e.g., articles, videos), and favored communication channels. Lastly is customer behavior data which includes website clicks, page visits, time spent on site, cart abandonment rates, email open and click-through rates, and social media interactions.

Segmentation can be divided up almost any number of ways; let’s look at a few of the most effective:

  • Geographic Segmentation (Also Known as Geotargeting) – Customers categorized by country, region, city, climate, or population density.

  • Customer Lifecycle Segmentation – Dividing your customer base into distinct segments based on where individuals are in their relationship with your company.

  • Purchase History Segmentation – As the name suggests, studying repetitive purchase habits makes it easier to predict future purchases.

  • Engagement-Based Segmentation – Identifying who is interacting with your brand and potentially more likely to convert.

When you’re ready to begin this process in full, read our guide on how to segment your email list.

Once you’ve studied your customer base, you can start grouping it by creating broad-level “personas” based on the specific data you’ve collected.

  • Using demographic data, you could create segments like "Young Professionals," "Parents," "Retirees," "Urban Dwellers," etc. This segmentation will inform future tailored email marketing strategies.

  • Based on preference data, you may create segments like "Tech Enthusiasts," "Health-Conscious," or "Fashion-forward”

  • Behavioral data may prompt customer segments like “Frequent Buyers,” “Occasional Shoppers,” “Cart Abandoners,” or “Loyal Customers”

Once you’ve identified your customer segments, you can start crafting content around product offerings that fit their precise interests, motivations, and pain points!

Understanding your target audience is the foundation of your marketing efforts and the main driver for meeting their specific needs and preferences through your email campaigns.

When you connect on a deeper level with potential customers and start building long-lasting relationships with existing ones, results are soon to follow.

Optimize Email For Mobile

It’s a mobile-first world and email has had a chance to blossom, wither, and evolve to host more opportunities than ever… if you know how to find them.

Even if you’re not a mobile-first company, you must treat your email campaigns with a mobile-first approach if you want any sort of sustained traction moving into the future. For instance, a study by Statista reveals that over 60% of Gen Z consumers prefer shopping on mobile devices, indicating the importance of mobile email optimization in reaching this audience. Knowing how to create dazzling email onboarding sequences and how to design responsive emails for mobile devices are great first steps to amplifying email campaign performance.

When looking at how to optimize email campaigns for mobile app users, it's important to gather and analyze specific customer data, including and beyond what we’ve mentioned above. Here are the most important types of customer data that mobile apps should consider when optimizing email campaign performance:

App Usage Patterns

Understanding the ways in which people use your app enables you to tailor email campaigns with timely content and relevant offers that align with their preferences and behavior for increased engagement and conversions. This includes:

  • Frequency of App Usage: How often users open the app.

  • Time Spent in App: The duration of user sessions within the app.

  • Popular Features: Which app features or sections users interact with the most.

In-App Behavior

Studying the nuances of what users are doing once they’re inside your app allows you to craft highly personalized email campaigns that showcase relevant products, address abandoned carts, and provide tailored content to drive conversions and enhance user engagement. Consider the following in-app behaviors to take note of:

  • Products or Services Viewed: Identify the specific items users are interested in.

  • Cart and Wishlist Activity: Track items added to the cart or wishlist.

  • Purchases: Record the products or services users have bought.

  • Abandoned Carts: Note items left in the cart without completing a purchase.

  • Content Consumption: Monitor which articles, videos, or content users engage with.

Location Data

We mentioned it above, but it’s worth repeating here! Accurate geo-segmentation data helps you deliver offers aligned with recipients’ local context and time zones for increased resonance and engagement.

  • Geographic Location: Tailor emails based on users' geographic regions or time zones.

  • Geo-targeted Offers: Provide location-specific promotions or events.

Preferences and Opt-ins

  • Communication Preferences: Understand whether users prefer email notifications.

  • Opt-in Status: Respect users' preferences for receiving marketing communications.

Device Information

  • Device Type: Optimize email content for the devices users are most likely to use.

App Version and Updates

  • App Version: Ensure users are aware of updates, new features, or improvements.

Data is the most valuable goldmine for understanding your target audience. Utilize advanced messaging analytics tools to gather actionable insights from your website, mobile app, and email campaigns. Track user interactions, measure engagement metrics, and segment your audience based on their preferences.

Knowing where your customers have been is one thing. Knowing where future ones will be is key if you wish to improve email performance.

Mobile Responsiveness – The Modern Take on Email Optimization

With a significant portion of emails being opened on mobile devices, it’s crucial to ensure that your email design is responsive and adapts to various screen sizes. Mobile-friendly emails lead to a better user experience, higher engagement, and improved conversion rates.

Leverage these strategies to enhance mobile responsiveness:

Use Responsive Design

Design your emails using responsive templates or fluid grid systems that automatically adjust to different screen sizes, ensuring a seamless experience across devices. Use a single-column layout so your emails adapt more effectively to narrower mobile screens, making content easy to read and navigate.

Choose fonts that are legible on smaller screens. Stick to web-safe fonts and avoid tiny font sizes. Consider using a font size of at least 14px for body text.

Remember, as a rule of thumb, the thumb always rules! Create buttons that are large enough to be tapped easily with a thumb and leave enough space around buttons to prevent accidental clicks.

You’ll also want to optimize email images for faster loading times. Use compressed and appropriately sized images. Don’t forget to use alt text for images to provide appropriate context if they don't load.

Have you optimized your mobile emails for Dark Mode yet? 81.9% of participants use Dark Mode on their phones, in apps, and wherever else it’s available.

Mobile-Friendly Reminders!

Avoid these common pitfalls when designing your responsive email campaigns…

  • While you want to ensure that recipients can pinch-to-zoom if necessary, especially for content like maps or detailed images, avoid relying on zooming for essential content readability.

  • Prioritize vertical scrolling over horizontal scrolling, as it's more intuitive on mobile devices.

  • Hover effects (like tooltips) don't work on mobile devices. Test that any content or information triggered by hover is accessible and visible without hovering.

  • Consider accessibility! Make sure touch interactions are accessible to users with disabilities by testing with assistive technologies, such as screen readers or voice commands.

Preview on Mobile

Always preview your emails on various mobile devices and email clients to ensure they display correctly and are easy to navigate. This includes the latest Apple devices (iPhone and iPad), popular Android devices (Samsung Galaxy, Google Pixel, OnePlus), and all major email clients:

  • Apple Mail (iOS)

  • Gmail (Android and iOS)

  • Outlook (Android and iOS)

  • Yahoo Mail (Android and iOS)

  • Samsung Email (Android)

  • Microsoft Outlook (Windows Phone)

Test, Test, Test

You must always be testing how interactive elements (buttons, links, sliders) respond to touch gestures to ensure a smooth user experience.

This includes things like swipe gestures and accordion sections. If your email includes carousels, image galleries, or other swipeable content, test swipe gestures to ensure smooth navigation between items. If you use expandable or accordion sections, test that they open and close easily with a tap — without any glitches or delays.

Optimize For Email Deliverability

Email deliverability describes your emails’ ability to reach the right inboxes (your targeted users) at the right time (precisely when you schedule them.) Several factors may impact your marketing email deliverability and you need a firm grasp on all of them if you are learning the ropes of email performance optimization.

1. Sender Reputation

The reputation of your domain and IP address plays a significant role in email deliverability. Email service providers (ESPs) and internet service providers (ISPs) use sender reputation as a key factor in determining whether an email should be delivered to the inbox or marked as spam. How do you improve your sender reputation?

By adhering to these best practices, you can strengthen your sender reputation, establish trust with ISPs, and ultimately ensure your emails reach the intended recipients' inboxes, improving email deliverability.

  • Maintain Healthy List Hygiene: Regularly clean your email list by removing inactive and unengaged subscribers to reduce bounce rates and spam complaints.

  • Send Relevant and Valuable Content: Provide content that aligns with recipient expectations, encouraging higher engagement and reducing the likelihood of being marked as spam.

  • Use Double Opt-In: Implement a double opt-in process to verify and confirm subscribers, ensuring you have explicit permission to send emails.

  • Authenticate Your Domain: Set up authentication mechanisms like SPF, DKIM, and DMARC to verify your domain and prevent spoofing. When you’re ready to learn the ins and outs of email authentication protocols, check out our guide on how and why to set up DMARC for email marketing.

  • Monitor Feedback Loops: Pay attention to feedback loops provided by ISPs, which inform you of spam complaints, enabling you to address issues promptly.

  • Segment and Personalize: Send targeted content based on recipient preferences and behaviors, fostering engagement and reducing the likelihood of unsubscribes.

  • Handle Unsubscribes Promptly: Honor unsubscribe requests immediately to avoid complaints and improve recipient satisfaction.

  • Monitor Metrics: Regularly track key email metrics like open rates, click-through rates, and spam complaints to identify areas for improvement.

  • Manage Complaints: Implement a clear and easy process for recipients to report issues, reducing the chances of them marking your emails as spam.

  • Engage and Interact: Encourage recipients to reply or interact with your emails, as genuine engagement contributes positively to your sender reputation.

Are you dealing with an email bounce problem? It may be time to take a comprehensive look at why emails bounce to get yourself back on track.

2. Email Volume and Frequency

Sending an excessive number of emails or bombarding recipients with too many emails in a short period can raise red flags for ISPs and lead to emails being filtered as spam. Finding the right balance in email frequency requires careful management to maintain engagement and prevent negative user reactions.

  • Gradual Scaling: Gradually increase your email volume over time to establish a consistent sending pattern and avoid sudden spikes that might trigger spam filters. If you haven’t taught yourself about email warm-up campaigns, now is the time!

  • Preference Management: Provide subscribers with the option to choose their preferred email frequency and types of content, ensuring that you align with their expectations and preferences.

  • Testing and Optimization: Regularly A/B test different email frequencies and observe how engagement metrics (open rates, click-through rates) and unsubscribe rates are affected. Optimize based on the results.

  • Monitoring and Adjusting: Continuously monitor your deliverability metrics and adjust your email volume and frequency based on recipient engagement and feedback, ensuring a positive user experience.

3. Compliance with Email Regulations

Adhering to email marketing regulations, such as GDPR (General Data Protection Regulation) in Europe and CAN-SPAM (Controlling the Assault of Non-Solicited Pornography And Marketing) in the United States, is essential for maintaining good deliverability. Failing to comply with these regulations can result in emails being blocked or marked as spam, not to mention the hefty financial penalties involved!

Best practices for email deliverability as outlined by GDPR and CAN-SPAM focus on ensuring compliance with regulations while maintaining a good sender reputation and respecting recipients' rights and preferences. Here's a brief overview:


  • Explicit Consent: Obtain explicit and informed consent from recipients before sending marketing emails. Clearly explain how their data will be used and provide an easy way to opt in.

  • Transparency: Clearly state your identity and contact details in your emails. Inform recipients about their rights to access, rectify, and erase their data.

  • Data Minimization: Only collect and process the data necessary for your email campaigns. Avoid excessive data collection.

  • Unsubscribe: Provide a clear and easily accessible unsubscribe option in your emails. Honor unsubscribe requests promptly.

  • Data Transfer: If transferring data outside the EU, ensure adequate safeguards are in place, such as Privacy Shield certification or standard contractual clauses.


  • Clear Identification: Clearly identify your email as an advertisement and include accurate sender information.

  • Opt-Out Mechanism: Provide a functioning "unsubscribe" option that allows recipients to opt out of future emails. Process opt-out requests within 10 business days.

  • Physical Address: Include your valid physical postal address in your emails.

  • Subject Line Accuracy: Avoid deceptive or misleading subject lines that might misrepresent the content of your emails.

  • Third-Party Compliance: Ensure third-party vendors and partners comply with CAN-SPAM regulations when sending emails on your behalf.

We encourage you to explore more about OneSignal’s relationship with GDPR and email compliance.

Optimize Email Content

This is where the rubber meets the road. No matter how stylish and optimized your emails are, uninspired writing won’t inspire action. Your email content must be crafted with the intent to engage. Let’s touch on a few basic email marketing tips.

Writing Effective Subject Lines and Preheaders

An attention-grabbing subject line and actionable preheader can simultaneously engage and intrigue recipients. It’s no easy balance to strike and one that requires a nuanced knowledge of how to optimize emails for conversions.

Some of your users may be receiving hundreds of emails every single day. Your subject line and preheader are your first (and likely only) chances to stand out from the inbox. Your email subject lines and preheaders should be brief, personalized, emphasize scarcity, and avoid spam trigger words.

Example of a strong subject line and pre-header:

Subject Line: "Your Invitation: Join Us for an Exclusive Webinar"

Pre-Header: "Register now to secure your spot at this insightful event."

Good subject lines and pre-headers are specific, relevant, and enticing, providing recipients with a clear reason to open the email. They convey value, urgency, or curiosity while complementing each other.

Example of a poor subject line and pre-header:

Subject Line: "Open for Exciting News"

Pre-Header: "See what we have in store for you."

Poor examples lack clarity, fail to offer value, and may come across as generic or uninteresting.

Above, we mentioned spam trigger words. These are words or phrases that can negatively effect the deliverability of your email campaigns, harming your reputation with ESPs and causing your emails to go straight to user spam folders.

Let’s look at some common email spam trigger words. It's important to note that the context and combination of words matter. While using these trigger words in isolation may not automatically result in spam classification, it's a good practice to avoid using them excessively or in a way that may raise suspicions. Always focus on providing valuable and relevant content to your subscribers to maintain a positive sender reputation and improve email deliverability.

  • Free: Promising something for free can trigger spam filters, as it's often associated with deceptive or unsolicited offers.

  • Urgent: Excessive use of urgency can make your email appear manipulative or sensationalized.

  • Limited Time: Similar to "urgent," this phrase can trigger spam filters due to its frequent use in spammy promotions.

  • Act Now: Encouraging immediate action can be perceived as pushy or misleading.

  • Guarantee: Excessive use of guarantees can raise skepticism and trigger spam filters.

  • Congratulations: This word is often used in phishing and scam emails.

  • Winning: Like "congratulations," this term is often associated with scams and misleading offers.

  • Cash: Financial-related terms can trigger spam filters due to their use in phishing attempts.

  • $$$: Symbols and excessive use of dollar signs can make your email look like a get-rich-quick scheme.

  • Earn Money: Similar to "cash," this phrase can be seen as promoting dubious income opportunities.

  • Discount: While not inherently bad, excessive use of discount-related terms can trigger spam filters.

  • Credit Card Offers: Phrases related to credit card offers can raise red flags in spam filters.

  • Satisfaction Guaranteed: Excessive use of this phrase can seem unrealistic and raise suspicion.

Ready to start getting creative? Review our 10 tips for writing high-performing email subject lines and preheaders.

Reminder! If you’re on the fence about which tone of voice, emoji, or graphic element to incorporate into your email campaigns, consider A/B testing different versions to a live audience to optimize email campaign performance!

Length and Formatting Best Practices

When it comes to email content, brevity is key. Yes, email copy has fewer length restrictions than ad copy or social media posts, but resist the urge to word-vomit your promotions to users with repetitive details. People have limited time and attention spans, so keeping your emails concise and to the point is crucial for making a lasting impression.

Keep subject lines concise and attention-grabbing, ideally around 6-10 words or 40-50 characters. This helps ensure that the subject line is fully visible on various devices and doesn't get cut off.

Aim for a preview text or pre-header length of around 35-75 characters. Make it compelling and relevant to entice recipients to open the email.

For the main copy of most marketing emails, a total word count of 150-500 words is a good starting point. However, you can go longer for more detailed content if it remains engaging.

Don’t forget to consider the mobile reading experience! Mobile users tend to skim, so use concise paragraphs, subheadings, and bullet points to break up content.

Keep your main call to action concise and actionable, around 2-5 words. Provide a clear next step for the recipient to take.

Lastly, include your most important links “above the scroll” (in the first three lines of copy or so) and focus on a few key benefits rather than a laundry list of features. Remember, less is more, and a well-formatted email ensures that your message gets across effortlessly.

Machine learning and AI tools are here to stay, mine as well use them to your advantage. Check out some crafty tips on using ChatGPT to help optimize your email campaigns.

Clear Call-to-Action

A clear Call-to-Action (CTA) is the heart of effective email content. Be explicit about what you want the reader to do next, whether it's clicking a link, making a purchase, or filling out a form. Use action-oriented language that instills a sense of urgency and emphasizes the benefits of taking action.

Strong CTA: "Download Your Free E-Book"

Specifies the benefit (free e-book) and encourages immediate action

Weak CTA: “Read Now”

Doesn't convey the content's value or what will be read.

Consider placing the CTA strategically, such as at the end of the email or even repeated throughout the content if it's a lengthy email. A prominent, well-designed CTA increases the chances of the reader engaging with your content and converting.

Looking for email marketing tips on how to write better CTAs? We got you covered.

Tailor Emails to the Customer Journey

Understanding your audience's customer journey stage is vital for crafting effective email content. Newer customers have completely different wants and needs than veteran followers of your brand — it’s important to respect those differences in your communication.

  • For prospects in the awareness stage, focus on educating and providing valuable information related to their pain points.

  • In the consideration stage, emphasize how your product or service solves their specific problems.

  • For customers in the decision or purchase stage, offer compelling offers and incentives to encourage conversion.

Personalize the content based on the recipient's past interactions and preferences, addressing their specific concerns and aspirations. Speak directly to their interests and desires to build a strong emotional connection and drive action.

Copywriting Tone – Best Practices

We’ve barely scratched the surface of writing effective email content. Matching your brand identity to your email copywriting style is essential for creating a consistent and cohesive customer experience. Here are some email marketing copywriting tips along with examples:

Understand Your Brand Voice

Before you start writing, define your brand voice – is it casual, formal, playful, authoritative?

Example: If your brand is known for its friendly and approachable tone, your email copy may use greetings like "Hey there!" or "We're excited to share..."

Use Consistent Language

Use the same terminology, phrases, and jargon that your brand uses across all communication channels to reinforce your brand identity.

Example: If your brand emphasizes eco-friendliness, use terms like "sustainable," "green," or "earth-friendly" consistently in your email copy.

Reflect Brand Values

Incorporate your brand's core values and mission into your email content to reinforce what your brand stands for.

Example: If your brand values adventure and exploration, you could use phrases like "embark on a journey" or "discover new horizons" in your emails.

Consistent Tone and Mood

Maintain a consistent emotional tone – whether it's uplifting, empathetic, humorous, or serious – that resonates with your brand and audience.

Example: If your brand is all about joy and positivity, your email copy could use phrases like "spread the happiness" or "brighten your day."

Social Proof

Integrate your brand's origin story, customer success stories, or anecdotes that embody your brand values into your email content.

Example: Share a customer's experience in an email, highlighting how your product positively impacted their life in line with your brand identity.

Visual and Verbal Consistency

Ensure that the visual elements (colors, fonts, images) used in your emails match your brand's visual identity, complementing the verbal tone.

Example: If your brand uses a minimalistic design with clean lines and neutral colors, your email design and copy should reflect simplicity and elegance.

Share Your Story

Use a tone that resonates with your target audience and feels authentic. Inject creativity and storytelling to make your message memorable and relatable.

Example: If your brand is known for innovation and pushing boundaries, craft an email that shares the journey of how your latest product evolved from an idea to a groundbreaking solution, using vivid language and narrative elements

Be Value-First

Highlight the value proposition and benefits of your offering to address the "What's in it for me?" question.

Example: If your brand emphasizes simplicity and convenience, structure your email copy to emphasize how your product's streamlined features can save time and effort for the recipient.

Optimize Send Time and Frequency

Sending your marketing emails at the right time can make a huge difference in engagement. Emails sent at the optimal time can lead to an increase in open rates and click-through rates. Timing matters because you want your emails to hit the recipient's inbox when they're most likely to check their emails and be receptive to your message.

By nailing the send time, you increase the chances of your emails being seen, read, and acted upon.

How do You Test Different Send Times and Days of the Week?

Testing different send times and days is easier than you might think! Start by segmenting your email list into smaller groups and sending the same email at different times to each group. You can try sending emails on weekdays versus weekends, during mornings, afternoons, or evenings. Use an email marketing platform that offers A/B testing capabilities to track the results. Monitor open rates, click-through rates, and conversions for each test group. Over time, you'll gather valuable data to pinpoint the optimal send times that resonate best with your audience.

Email frequency is a balancing act — send too often, and you risk overwhelming subscribers, send too infrequently, and you might miss out on opportunities. To align send time with audience behavior, observe engagement patterns. Additionally, consider their preferences by asking for feedback through surveys or monitoring response times to previous emails.

What is the Best Time to Send Emails?

Different industries have distinct audience behaviors and preferences. For instance, a B2B software company may find that sending emails during business hours on weekdays garners better results, while an online retailer might see higher engagement on weekends when shoppers have more time to browse and make purchase decisions. Understanding your audience's behavior and preferences will help you tailor your email marketing strategy for maximum impact.

According to Indeed, the best time for most industries to send marketing emails is Monday, Tuesday, or Thursday around 10 am. Mid-morning emails have a higher chance of catching recipients at the start of their day or on their first phone breaks from work.

Tracking Email Performance

Tracking email performance is the only way to assess your email marketing strategy. Data-driven insights will help you identify where you went wrong (if anywhere) and inform future decisions on email performance optimization. Most importantly, tracking email performance allows you to measure the return on investment (ROI) of your email marketing campaigns and ensures that you are delivering valuable and engaging content to your subscribers.

Which Email KPIs Should You Be Focused on Most to Improve Email Performance?

The short answer? Open rates and click-through rates are your best friends. Open rates indicate how many recipients opened your email, giving you an initial measure of its effectiveness and subject line appeal. Click-through rates measure the percentage of recipients who clicked on a link within your email, demonstrating engagement and interest in your content.

Other email KPIs to be aware of include:

  • Conversion Rate: The percentage of recipients who completed the desired action, such as making a purchase or filling out a form.

  • Bounce Rate: The percentage of emails that were not delivered to the recipient's inbox due to invalid or inactive email addresses, impacting deliverability.

  • Unsubscribe Rate: The percentage of recipients who chose to unsubscribe from your email list, indicating disinterest or dissatisfaction with your content.

  • Spam Complaint Rate: The percentage of recipients who marked your email as spam, affecting sender reputation and deliverability.

  • Revenue per Email: The amount of revenue generated per email sent, providing insight into the financial impact of your email campaign performance.

  • List Growth Rate: The rate at which your email list is growing, indicating the effectiveness of your lead generation efforts.

Maintaining a Healthy Email List

Part of the ongoing process of tracking email performance is maintaining a healthy email list. This includes housekeeping items like identifying and eliminating duplicate email addresses to ensure that each subscriber receives your content only once. Additionally, removing invalid email addresses that bounce back undeliverable messages enhances email deliverability and prevents potential spam issues.

Lastly, make sure to consistently remove subscribers who have not engaged with your emails for a significant period, ensuring that your list comprises active and interested recipients.

For an expanded look into email compliance, avoiding the spam folder, and navigating high bounce rates, we put together a guide to cleaning your email list!

A Platform That Brings Email Marketing to Every Device

You shouldn’t have to choose between overpriced email providers and email companies with restrictive feature limits. That’s why OneSignal offers an email composer, automation suite, and template library designed to compete in a mobile-first marketplace. Our no-code editor gives you full control over your campaigns, including custom audience segmentation.

Try OneSignal Email for Free!