In a previous article, we explored how to create an effective corporate newsletter—focusing on its structure, content, and purpose.
Creating a solid newsletter is only the first step.
In this article, we focus on two key factors that can significantly boost its performance: A/B testing and best practices for avoiding spam filters—two levers that often determine whether your newsletter gets ignored or delivers real value to your business.
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According to a study by Invesp, A/B testing is the second most commonly used method for improving conversion rates—right after customer journey analysis.
Around 59% of the companies surveyed regularly run tests on their marketing emails.
A/B testing a newsletter means sending out two slightly different versions of the same email to see which one performs better against a specific goal—whether it’s open rate, click-through rate, or conversions.
The process is straightforward: you take a small sample from your contact list and split it into two similar groups. One group receives version A, the other version B. After a set amount of time, you analyze the results and send the winning version to the rest of your audience.
The key is to test one variable at a time. This ensures you can clearly identify what influenced the results. There are many elements you can experiment with, such as:
But what’s the real value of an A/B test?
The goal isn’t to discover a “magic formula,” but to observe real behavior, gather meaningful signals, and gradually understand what makes a corporate newsletter more effective, more engaging, and more widely read.
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All the effort, from defining goals to refining content and running A/B tests, is only worthwhile if your newsletter actually reaches its destination. Because before it can be read, a newsletter needs to clear the most basic—and often most unforgiving—hurdle: the spam filter.
According to a study by Return Path, only 79% of marketing emails worldwide make it to the inbox. In other words, one out of five gets blocked or lands directly in the spam folder, never even getting the chance to be read.
Email providers like Gmail, Outlook, and Yahoo use increasingly sophisticated algorithms to flag unwanted messages. That’s why it’s critical to follow a set of best practices to ensure your corporate newsletter gets delivered to the primary inbox—not buried in the “Promotions” tab or flagged as spam.
The first key element is the subject line: it needs to be clear and engaging, but never aggressive. Words like “buy now,” excessive capitalization, or too many exclamation marks are red flags for spam filters. Similarly, a newsletter made up almost entirely of images—or with an imbalanced text-to-image ratio—can be seen as suspicious.
Spam filters look for credible, readable content. This is why adding alternative text (alt text) to every image is important—not just for accessibility, but because many email platforms block images by default.
Consent is another essential factor. Only send communications to users who have explicitly opted in. This isn’t just a legal requirement, it’s also critical for protecting your brand’s sender reputation. Spam complaints have a serious impact on your future deliverability. For the same reason, always include a clear, easy-to-use unsubscribe link that actually works.
Be mindful of the sender name and email address as well. Using a verified company domain, rather than a free email service, builds trust and increases the chances of delivery. Another common misstep is sending too many emails too frequently. Overloading your contacts with irrelevant messages leads quickly to unsubscribes and spam reports.
It’s better to send one less newsletter than one too many. Focus on being anticipated, recognizable, and genuinely useful.
Lastly, be cautious with the links you include. Avoid shortened URLs, overly complex strings, or links that don’t clearly match the content. Both spam filters and recipients are quick to flag them as suspicious.
Using a reliable, professional email platform is the technical foundation for everything else. A solid infrastructure improves your chances of reaching the inbox, protects you from blacklists, and gives you the tools to track performance effectively
For companies looking to build a data-driven and effective email marketing strategy, HubSpot offers a comprehensive and highly reliable solution. More than just a CMS, HubSpot is an integrated platform that allows you to manage, monitor, and optimize the entire lifecycle of your corporate newsletters—with tools designed to ensure high performance and maximum deliverability.
Its automated A/B testing feature enables you to precisely test individual variables, such as subject line, content, or call to action, and measure their effectiveness in real time through advanced reports and intuitive dashboards. HubSpot also provides a complete toolkit to support your A/B testing efforts.
At the same time, the platform includes essential technical features to improve email deliverability, such as domain authentication, HTML validation, spam complaint monitoring, and adherence to email-sending best practices.
Native integration with the CRM allows for accurate audience segmentation, content personalization, and the creation of automated workflows, ensuring each email is relevant and meaningful to its recipient. While no platform can fully eliminate the risk of spam, HubSpot equips you with all the necessary tools to minimize that risk and build a strong, professional sender reputation over time.
Ander Group, as HubSpot Platinum Partner, can support you across the entire process: from A/B testing to spam prevention, helping you build high-performing newsletters that deliver measurable results and strengthen the connection with your audience.