Should I include List-Unsubscribe headers in transactional emails and what are the DKIM best practices?
Michael Ko
Co-founder & CEO, Suped
Published 10 May 2025
Updated 19 Aug 2025
9 min read
Navigating the complexities of email deliverability often brings up questions about seemingly contradictory best practices. Two common areas of inquiry revolve around including List-Unsubscribe headers in transactional emails and defining optimal DKIM signing practices. I've often heard these concerns, especially from senders managing mixed email streams, where marketing and transactional messages originate from the same IPs. The prevailing thought used to be that transactional emails, by their nature, didn't require an unsubscribe option, but recent developments have shifted this perspective significantly.
My experience shows that adhering to modern best practices is crucial for maintaining a strong sender reputation and ensuring high inbox placement rates. Ignoring evolving standards, especially those set by major mailbox providers like Google and Yahoo, can lead to deliverability issues. This article will explore why it's beneficial to include List-Unsubscribe headers in transactional emails and detail the best practices for your DKIM configuration to boost your email deliverability.
Why List-Unsubscribe matters for transactional emails
The traditional view was that transactional emails, such as password resets or order confirmations, did not need an unsubscribe link because they were essential for the user's interaction with a service. Unlike marketing emails, which are explicitly opted into for promotional content, transactional emails were considered non-commercial and often exempt from certain unsubscribe requirements. However, this distinction has blurred.
Mailbox providers are increasingly prioritizing user experience and control over their inboxes. If a recipient perceives an email as unwanted, regardless of its 'transactional' label, they are likely to mark it as spam. A spam complaint is far more damaging to your sender reputation and IP standing than an unsubscribe request. This is why even for transactional emails, providing an easy way to opt-out is becoming a best practice. It helps avoid spam complaints and supports a healthier sending ecosystem.
The introduction of new sender requirements by major mailbox providers, like Google’s and Yahoo’s updated guidelines, has pushed the List-Unsubscribe header from a recommendation to a near necessity for high-volume senders, even for some transactional emails. While the explicit mandate primarily targets bulk senders and marketing emails, its broad adoption by mailbox providers means that including it across the board can safeguard your deliverability. Learn more about how these headers function with one-click, mailto, and HTTP links, and their implications for sender reputation.
Implementing List-Unsubscribe headers
The impact on deliverability
When recipients have an easy way to unsubscribe, they are less likely to mark your emails as spam. This directly improves your spam complaint rates, a key metric mailbox providers use to evaluate your sender reputation. A lower complaint rate leads to better inbox placement for all your emails, transactional or otherwise.
Reputation boost: Reduces spam complaints, which are more damaging than unsubscribes.
User control: Provides recipients with a clear path to opt-out, even from unwanted transactional messages like unsolicited password resets. This also improves the user experience.
The List-Unsubscribe header enables one-click unsubscribe functionality, often presented as a prominent button by mailbox providers like Outlook and Yahoo Mail. This convenience drastically reduces the likelihood of a recipient marking your email as spam simply because they can't find an unsubscribe link in the message body. While it might seem counterintuitive to offer an unsubscribe option for essential transactional emails (like a password reset), it's a proactive measure to manage user preferences and prevent reputation damage.
Implementing the List-Unsubscribe header involves adding specific lines to your email's header. This typically includes a mailto: link for simpler, automated unsubscribes and an http(s):// URL for a web-based unsubscribe page, allowing for more granular control, such as a preference center. The RFC 8058 standard specifies the List-Unsubscribe-Post header for true one-click functionality, where the unsubscribe action is processed automatically without needing to visit a page. This is critical for meeting the latest requirements. To verify if your company's emails have List-Unsubscribeheaders correctly configured, you can inspect the raw email headers.
DKIM (DomainKeys Identified Mail) is an email authentication method that uses cryptographic signatures to verify that an email message was not altered in transit and that it genuinely came from the claimed sender. It's a cornerstone of modern email security and essential for email deliverability. Mailbox providers use DKIM to confirm the legitimacy of your emails, helping to prevent spoofing and phishing attacks. You can find out more about DMARC, SPF, and DKIM.
The core of DKIM best practices lies in what headers you choose to sign. While the From header is mandatory for signing, oversigning (including many headers in the DKIM signature) is generally recommended. This practice ensures that even minor modifications to critical headers in transit will invalidate the signature, helping to protect your messages from tampering and improving your email deliverability.
Commonly signed headers include Subject, Date, To, and Message-ID. Importantly, for compliance with RFC 8058, your DKIM signature must cover both the List-Unsubscribe and List-Unsubscribe-Post headers when they are present. This ensures the integrity of the one-click unsubscribe mechanism. It is important that the DKIM domain needs to align with the List-Unsubscribe domain.
Beyond header selection, avoid using the l= tag in your DKIM configuration, which specifies the length of the signed body. This tag can lead to issues if the email body is altered even slightly. Consider using the x= tag to expire signatures, which can mitigate DKIM replay attacks.
The interplay of List-Unsubscribe and DKIM
While there is no explicit 'blessed list' of DKIM fields favored by all mailbox providers, the general consensus is to sign any header that is critical to the message's integrity or that could be spoofed. This includes headers like From, Subject, and Date, as well as any custom headers unique to your sending practices. For optimal email authentication, review our guide on setting up SPF, DKIM, and DMARC.
For transactional emails specifically, it’s worth signing headers like To, Cc, Bcc, Reply-To, In-Reply-To, and References, as these are unique and should not be modified. If you're using a third-party email service provider, check their documentation for recommended DKIM header signing practices, as they might have specific configurations for their systems. Generally, a comprehensive list of signed headers is beneficial for email security. More on DKIM and DMARC best practices is available.
I've personally found that the combination of properly configured DKIM and the inclusion of List-Unsubscribe headers significantly reduces the chance of emails landing in the spam folder, even for transactional messages. This proactive approach not only keeps you compliant with emerging standards but also signals to mailbox providers that you are a responsible sender committed to recipient satisfaction. This is crucial for avoiding being placed on a blacklist or blocklist.
Handling unsubscribes from transactional emails
Marketing emails
Marketing emails, by definition, require a clear unsubscribe option. Users opt-in to receive promotional content, and they must have an easy way to opt-out. Failure to provide this can lead to legal issues and severe deliverability problems. Implementing List-Unsubscribe is mandatory for bulk marketing sends.
Legal compliance: Required by regulations like CAN-SPAM, GDPR, and CASL.
Deliverability: Crucial for maintaining good sender reputation and avoiding blocklists.
User experience: Empowers recipients to control their inbox, reducing spam complaints.
Transactional emails
While not always legally mandated to include an unsubscribe link, adding a List-Unsubscribe header to transactional emails is now a strong recommendation. This is particularly true in light of new sender requirements from providers like Gmail that emphasize one-click unsubscribe for high-volume senders, irrespective of email type.
Spam prevention: Reduces spam complaints from users who perceive transactional emails as unwanted or suspicious.
Misdirected emails: Offers a way out for recipients who receive transactional emails due to a mistyped email address or fraudulent sign-ups. More on transactional emails and unsubscribe links.
Holistic approach: Contributes to a consistent and positive sending reputation across all email types.
When an unsubscribe request comes in for a transactional email, it’s important to have a clear policy on how to handle it. For critical transactional messages, such as password resets or security alerts, you might not want to suppress all communication. However, for less critical transactional emails (e.g., promotional newsletters mixed with account updates), you should consider a granular approach to suppression. This could involve suppressing marketing and less critical transactional messages, while still allowing vital communications to reach the recipient. Always prioritize user safety and privacy. Learn more about the impact on email reputation.
A “this isn’t me” option within your unsubscribe flow, or even tied to the List-Unsubscribe header, could be a valuable addition. This allows recipients who received an email due to a mistyped address (or a malicious sign-up) to flag it without a full unsubscribe, providing valuable data about invalid addresses while protecting your reputation.
Final thoughts on deliverability
The evolving landscape of email deliverability demands a holistic approach. Including List-Unsubscribe headers in transactional emails, alongside robust DKIM implementation, is no longer just a recommendation, it is essential. These practices collectively enhance your sender reputation, reduce spam complaints, and ensure your legitimate emails reach the inbox.
By proactively adopting these measures, you signal to mailbox providers that you are a responsible sender committed to maintaining a clean and trustworthy email ecosystem. This commitment directly translates to improved deliverability across all your email campaigns, whether marketing or transactional. For more insights on how List-Unsubscribeheaders affect email deliverability with a preference center, consult our detailed guide.
Regularly monitor your deliverability metrics, including spam complaint rates and inbox placement. Utilize tools like Google Postmaster Tools to track your domain and IP reputation. Staying informed and proactive is the key to navigating the ever-changing landscape of email deliverability in 2025 and beyond. If you are still seeing your emails going to spam, consider our guide on how to fix it.
Views from the trenches
Best practices
Always include both List-Unsubscribe and List-Unsubscribe-Post headers in your emails.
Ensure your DKIM signature covers both List-Unsubscribe headers.
Define a clear policy for handling unsubscribe requests from transactional emails.
Common pitfalls
Not including List-Unsubscribe headers on transactional emails, leading to spam complaints.
DKIM signatures that do not cover critical headers, making emails vulnerable to tampering.
Failing to process unsubscribe requests promptly, which can damage sender reputation.
Expert tips
Consider adding a 'this isn't me' option to help manage misdirected emails.
Regularly monitor your email deliverability and sender reputation metrics.
Communicate clearly with recipients about why they receive transactional emails.
Expert view
Expert from Email Geeks says RFC 8058 requires the List-Unsubscribe header to be signed by DKIM, and both Google and Yahoo recommend including it even for opted-in emails to provide an easy opt-out.
2024-11-04 - Email Geeks
Expert view
Expert from Email Geeks says there is no downside to allowing recipients to opt out from any message they might otherwise report as spam.
Google and 
Yahoo, can lead to deliverability issues. This article will explore why it's beneficial to include List-Unsubscribe headers in transactional emails and detail the best practices for your DKIM configuration to boost your email deliverability.
Outlook and 
Yahoo Mail. This convenience drastically reduces the likelihood of a recipient marking your email as spam simply because they can't find an unsubscribe link in the message body. While it might seem counterintuitive to offer an unsubscribe option for essential transactional emails (like a password reset), it's a proactive measure to manage user preferences and prevent reputation damage.
Gmail that emphasize one-click unsubscribe for high-volume senders, irrespective of email type.
Google Postmaster Tools to track your domain and IP reputation. Staying informed and proactive is the key to navigating the ever-changing landscape of email deliverability in 2025 and beyond. If you are still seeing your emails going to spam, consider our guide on how to fix it.
