What is the deliverability impact of non-HTTPS engagement tracking in email marketing?
Michael Ko
Co-founder & CEO, Suped
Published 17 Jul 2025
Updated 15 Aug 2025
8 min read
The digital landscape increasingly emphasizes security, and email marketing is no exception. With browsers and mailbox providers prioritizing user safety, the shift from HTTP to HTTPS has become a fundamental requirement for websites and, by extension, for effective email campaigns. While the direct deliverability impact of non-HTTPS engagement tracking might not always be immediately obvious in every single metric, it creates a subtle yet significant erosion of trust and functionality that ultimately affects your ability to reach the inbox.
When your email's tracking pixels or click-through links use HTTP instead of HTTPS, they signal an outdated approach to security. This can lead to issues with how your emails are rendered, how accurately engagement is recorded, and how mailbox providers perceive your sending practices. Modern email ecosystems are designed to prioritize secure connections, and anything less can put your email program at a disadvantage.
My goal here is to explain the nuances of why non-HTTPS engagement tracking can hurt your email deliverability, even if it's not always a direct block. It is about understanding the cumulative effects on sender reputation, user experience, and ultimately, your campaign performance.
The evolution of internet security and email
Historically, email tracking relied on simple, often non-secure, methods like tiny 1x1 pixel images or redirects. However, the internet has moved significantly towards HTTPS encryption for all web traffic to protect user data and ensure privacy. This shift has not bypassed email. Major players like Google have been particularly vocal about deprecating mixed content, where a secure (HTTPS) page loads insecure (HTTP) resources. This directly impacts email, as emails are essentially HTML pages rendered within a client.
When an email client, especially a webmail interface like Gmail, renders an email that contains an HTTP tracking pixel or link, it's considered mixed content. Browsers and mail clients are increasingly blocking such content by default or warning users about it. This means your tracking pixel might not load, leading to inaccurate open rate data. Similarly, clicks on HTTP links might trigger security warnings, deterring users from proceeding. We have more information about how Chrome blocking mixed content affects email deliverability.
This movement towards a more secure web environment means that non-HTTPS tracking is not just a technical oversight, but a deliverability risk. Mailbox providers interpret the use of insecure elements as a potential sign of less reputable sending practices. Even if your content is legitimate, the technical implementation can trigger spam filters or lower your sender reputation. For more on this, consider reading about Google's stance on HTTPS for email marketers.
Consequences of insecure tracking on deliverability
Using HTTP for engagement tracking can impact your email deliverability in several ways, both directly and indirectly. These issues often compound, making it harder for your emails to consistently reach the inbox.
The primary direct impact is on engagement tracking itself. If tracking pixels are blocked due to mixed content warnings, your reported open rates will be artificially low. While open rates are becoming less reliable as a sole metric due to privacy changes like Apple's Mail Privacy Protection, inaccurate data can still lead to poor segmentation and campaign optimization decisions. This can ultimately affect your long-term sender reputation when you miss opportunities to send to engaged users, or you keep sending to unengaged subscribers, as explained in the deliverability consequences of decreasing metrics.
Furthermore, non-HTTPS links within your email can create a poor user experience. When a recipient clicks an HTTP link, they may encounter browser security warnings, or the link may simply not load. This immediately erodes trust and can lead to lower click-through rates. Mailbox providers monitor user engagement, and a lack of clicks or negative user interactions (like abandoning a page due to security warnings) can signal to them that your emails are not valuable or trustworthy, potentially harming your inbox placement. I have an article that goes deeper into the consequences of using non-HTTPS links in emails.
The problem
Mixed content warnings: Browsers and email clients may block insecure HTTP content within an HTTPS email.
Inaccurate tracking: Blocked pixels lead to misleading open rate data and incomplete engagement metrics.
Eroded trust: Security warnings or broken links make recipients distrust your brand, reducing future engagement.
Sender reputation impact: Low engagement and perceived insecurity can signal poor practices to ISPs.
Implementing HTTPS for tracking
Ensuring all aspects of your email marketing, including engagement tracking, use HTTPS is a non-negotiable best practice. If your email service provider (ESP) or marketing automation platform does not support HTTPS tracking out of the box, it is a significant limitation that needs addressing. Many vendors now offer custom tracking domains with SSL certificates, which is the ideal solution.
Implementing HTTPS for your tracking domains means that all open pixels and click-through links within your emails will be secure. This eliminates mixed content warnings, ensures accurate tracking, and builds trust with both recipients and mailbox providers. You can learn more about how secure HTTPS links improve email deliverability.
Beyond simply having HTTPS, it is also important to ensure your tracking URLs are aligned with your sending domain. This consistency reinforces your brand identity and further signals legitimacy to mailbox providers. An example of this is the case of SocketLabs, where secure engagement tracking helps solve Chrome image security issues. By taking these steps, you safeguard your sender reputation and improve your overall email deliverability, ensuring your messages land in the inbox as intended.
Sender reputation and user experience
Beyond the technical configurations, maintaining a strong sender reputation is crucial for deliverability. While HTTPS directly impacts how mailbox providers view your technical setup, it is also intrinsically linked to how recipients interact with your emails.
If your emails are consistently triggering security warnings or if tracking images fail to load, it will inevitably lead to lower engagement rates. Recipients are less likely to open future emails, click on links, or convert if their initial experience is negative. Low engagement is a red flag for Internet Service Providers (ISPs) and can result in your emails being directed to the spam folder or even put on a blocklist (or blacklist). This highlights the indirect but powerful impact of non-HTTPS tracking on your overall sender reputation.
By ensuring your engagement tracking is fully secured with HTTPS, you contribute positively to your sender reputation. It signals to mailbox providers that you adhere to modern security standards and care about your recipients' experience. This proactive approach helps avoid negative signals that could lead to your emails being filtered or blocked. I've covered the importance of SSL for tracked links and images in a previous article.
Views from the trenches
Best practices
Always ensure your email service provider (ESP) or marketing automation platform supports HTTPS for all tracking domains.
Configure a custom tracking domain with an SSL certificate to align with your sending domain.
Regularly monitor your email deliverability metrics, including open and click rates, for inconsistencies.
Use tools like Google Postmaster Tools to identify any unusual spikes in spam complaints.
Common pitfalls
Relying on default, often HTTP, tracking domains provided by legacy email platforms.
Ignoring browser warnings about mixed content, which can lead to blocked tracking pixels.
Failing to update your tracking infrastructure as web security standards evolve.
Assuming deliverability is solely about content, neglecting the technical underpinnings.
Expert tips
If your vendor does not support HTTPS for tracking, push them for an upgrade or seek alternative solutions.
Educate your team on the importance of HTTPS beyond just website security, extending it to email marketing.
When troubleshooting, verify both your sending domain and tracking domain have valid SSL certificates.
Periodically use an email deliverability tester to see how your emails render and track.
Expert view
Expert from Email Geeks says that isolating the exact deliverability impact of non-HTTPS engagement tracking is challenging because senders often neglect other best practices when they also fail to implement HTTPS. Therefore, a lack of HTTPS might be an indicator that other best practices are not being followed.
2020-10-06 - Email Geeks
Expert view
Expert from Email Geeks says that Chrome is actively moving away from showing mixed content like non-HTTPS images on an HTTPS page, which clearly indicates that Google considers this a significant issue for user experience and security.
2020-10-06 - Email Geeks
Summary of impacts and best practices
The deliverability impact of non-HTTPS engagement tracking in email marketing is multifaceted. While it may not always lead to an immediate hard bounce or direct placement on a blacklist, it chips away at your sender reputation and negatively affects how your emails are perceived and rendered by modern email clients.
In an era where security and user experience are paramount, relying on HTTP for any part of your email content or tracking is a significant oversight. Mailbox providers and browsers are increasingly stringent, pushing all traffic towards secure protocols. Adapting to this standard by implementing HTTPS for all engagement tracking is not just a best practice, but a necessity for maintaining strong deliverability and accurate campaign analytics.
Prioritizing HTTPS for your tracking domains ensures your emails look professional, perform as expected, and build the trust necessary for long-term email marketing success. It is an investment in your sender reputation and the overall health of your email program.
Google have been particularly vocal about deprecating mixed content, where a secure (HTTPS) page loads insecure (HTTP) resources. This directly impacts email, as emails are essentially HTML pages rendered within a client.
Gmail, renders an email that contains an HTTP tracking pixel or link, it's considered mixed content. Browsers and mail clients are increasingly blocking such content by default or warning users about it. This means your tracking pixel might not load, leading to inaccurate open rate data. Similarly, clicks on HTTP links might trigger security warnings, deterring users from proceeding. We have more information about how Chrome blocking mixed content affects email deliverability.
Apple's Mail Privacy Protection, inaccurate data can still lead to poor segmentation and campaign optimization decisions. This can ultimately affect your long-term sender reputation when you miss opportunities to send to engaged users, or you keep sending to unengaged subscribers, as explained in the deliverability consequences of decreasing metrics.
