How can I verify if my company's emails have List-Unsubscribe headers correctly configured?
Michael Ko
Co-founder & CEO, Suped
Published 4 Jun 2025
Updated 17 Aug 2025
7 min read
Ensuring your company’s emails have correctly configured List-Unsubscribe headers is crucial for email deliverability and maintaining a positive sender reputation. These headers provide a clear, simple way for recipients to opt out of your mailing lists, which in turn reduces spam complaints and helps your emails reach the inbox.
With major mailbox providers like Gmail and Yahoo implementing stricter sender requirements, including proper List-Unsubscribe implementation (especially RFC 8058 for one-click unsubscribe) is no longer optional for high-volume senders. Failing to meet these requirements can lead to significant deliverability issues, including your emails being routed to the spam folder or even blocked entirely.
This guide will walk you through the essential steps to verify that your List-Unsubscribe headers are set up correctly, ensuring compliance and improving your email program’s overall health.
Manual inspection of email headers
The most direct way to check for List-Unsubscribe headers is by inspecting the raw source of an email. When an email client like Gmail or Yahoo Mail displays a convenient 'Unsubscribe' link at the top of a message, it generally indicates that valid List-Unsubscribe headers are present. However, this visual cue is not always a definitive confirmation. Mailbox providers might sometimes display an unsubscribe button even if the underlying headers are not fully compliant, or conversely, they might not display the button even if valid headers exist.
To get a precise picture, you need to dig into the email's original source. This is typically accessible through a 'Show original' or 'View message details' option within your email client. Once you have the raw email, you can scan for specific header fields.
Look for the List-Unsubscribe and List-Unsubscribe-Post headers. The first header, List-Unsubscribe, typically contains a mailto: address and/or an HTTP URL. The List-Unsubscribe-Post header, as defined by RFC 8058, is what enables the one-click unsubscribe functionality, making it a critical component for modern email deliverability. You can learn more about how these headers function for sender reputation.
Using an email testing tool
While manual inspection is insightful, using an email testing tool provides a more comprehensive and automated verification. These tools analyze your email’s entire structure and headers, not just for List-Unsubscribe, but also for other crucial deliverability factors like SPF, DKIM, and DMARC.
To use a checker, you typically send a test email to a unique address provided by the tool. The tool then processes the email and presents a detailed report, indicating whether your List-Unsubscribe headers are correctly formatted and compliant with current standards. This is especially helpful for ensuring you meet Yahoo and Gmail’s requirements.
Such tools also identify other issues that could impact deliverability, such as broken links, image loading problems, or potential spam triggers. This holistic view helps you proactively address any issues that might lead to your emails being marked as spam or appearing on a blocklist (or blacklist).
Pros
Automation: Quickly processes emails for header validation.
Comprehensive report: Provides detailed insights beyond just unsubscribe headers.
Compliance check: Helps ensure adherence to industry standards like RFC 8058.
Cons
External reliance: You depend on the tool's accuracy and features.
Limited custom testing: May not cover highly specific or unique email configurations.
Testing the unsubscribe functionality
Once you’ve confirmed the presence of the List-Unsubscribe headers, the next critical step is to test the actual unsubscribe functionality. This ensures that when a user clicks the unsubscribe link or triggers the one-click unsubscribe action, they are successfully removed from your mailing list.
There are two main types of List-Unsubscribe methods to test, which include the mailto: and HTTP types. The mailto: method sends an email to a specific address to process the unsubscribe request. The HTTP method redirects the user to a webpage, often a preference center, where they can confirm their unsubscribe or manage subscriptions.
The one-click unsubscribe, which utilizes the List-Unsubscribe-Post header, is particularly important. This method allows the mailbox provider to send an automated POST request to the unsubscribe URL without the user needing to visit a landing page, providing a seamless unsubscribe experience. You can specifically test and validate this functionality to ensure it's working as expected.
Mailto: unsubscribe
Send a test email to an address that uses this method. Look for a confirmation email or check your unsubscribe list to confirm the address was removed.
HTTP URL unsubscribe
Click the unsubscribe link in a test email. Verify that you are redirected to the correct unsubscribe page and that the process completes successfully.
Checking with your email service provider (ESP)
Many email service providers (ESPs) and marketing automation platforms handle List-Unsubscribe headers automatically. If you’re using a reputable platform, it’s likely they already implement these headers by default as part of their deliverability best practices.
However, it's always a good idea to check your ESP’s documentation or settings to confirm. Some platforms might offer options to customize or enable/disable these headers, so understanding your platform’s capabilities is important. Ensuring these are configured correctly can also positively impact your email reputation.
If you manage your own email sending infrastructure or are using a custom solution, you’ll need to ensure these headers are manually added to your email templates. This involves including the correct header fields in the SMTP (Simple Mail Transfer Protocol) message.
Email platform
Likely default status
Additional considerations
Mailchimp
Automatically included.
Verify settings for one-click unsubscribe options. Mailchimp generally handles this well.
Klaviyo
Generally included.
They have been rolling out RFC 8058 compliance universally. Check your integration settings.
SendGrid
Included by default if unsubscribe tracking is enabled.
Ensure you have unsubscribe functionality enabled in your account settings.
Troubleshooting common issues
Even with correctly configured headers, sometimes the unsubscribe option might not appear as expected for recipients. This can be due to various reasons, from specific email client behaviors to subtle misconfigurations.
Mailbox providers have their own algorithms for determining when to display the unsubscribe button. While the presence of the List-Unsubscribe and List-Unsubscribe-Post headers is a strong signal, there’s no absolute guarantee it will always be displayed. Factors such as sender reputation, engagement rates, and even the user’s past interaction with similar emails can influence this. For example, some mail clients (like those from Microsoft) might have specific requirements or display policies.
Additionally, ensuring your email authentication records (SPF, DKIM, DMARC) are properly configured is vital. These records authenticate your emails and build trust with mailbox providers, which can indirectly affect how your List-Unsubscribe headers are recognized and processed. Keeping an eye on your blocklist monitoring is also important, as being on a blacklist can severely impact all aspects of your email deliverability, including unsubscribe header visibility.
Conclusion
To ensure your emails consistently reach the inbox and provide a great user experience, regularly verifying List-Unsubscribe headers is key. This not only helps you comply with major mailbox provider requirements but also improves your sender reputation by reducing spam complaints and fostering a healthier email ecosystem.
Combining manual header inspection with automated testing tools and regular functional checks will give you the most accurate assessment of your List-Unsubscribe configuration. This proactive approach ensures deliverability and compliance.
Views from the trenches
Best practices
Always include both `mailto:` and HTTP URL options in your List-Unsubscribe header for broader compatibility and user choice.
Implement the `List-Unsubscribe-Post` header (RFC 8058) to enable true one-click unsubscribe functionality.
Regularly monitor your email deliverability metrics, including spam complaint rates, in Google Postmaster Tools.
Common pitfalls
Relying solely on an email client's visible unsubscribe button as proof of correct header configuration.
Not regularly testing unsubscribe links, which can become broken or lead to non-compliant pages.
Ignoring `List-Unsubscribe-Post` leading to a less seamless one-click unsubscribe experience for users.
Expert tips
Use dedicated email testing tools to get a comprehensive report on your email headers and content.
Keep up-to-date with mailbox provider requirements, as these can change and impact header parsing.
Consider how List-Unsubscribe interacts with preference centers for a better user experience.
Expert view
Expert from Email Geeks says a tool like AboutMy.Email can verify the presence of List-Unsubscribe and List-Unsubscribe-Post headers, which are crucial for compliance.
2024-01-10 - Email Geeks
Expert view
Expert from Email Geeks says checking the full, raw email headers (often found via 'view original' in email clients) is essential to confirm List-Unsubscribe header presence, as relying on the visible unsubscribe link in the UI is not always sufficient.
Mailchimp
Klaviyo
SendGrid
