Does the order of mailto and https in List-Unsub header matter?

Key findings

• RFC 8058 compliance: RFC 8058, which defines one-click unsubscribe, mandates the presence of an https URL but does not specify any particular order for multiple links.
• Client preference: Modern email clients supporting one-click unsubscribe will prioritize the https link over mailto, regardless of the order they appear in the header.
• Fallback option: Including a mailto link alongside the https URL provides a fallback for older clients or those that do not fully support RFC 8058.
• No adverse impact: The specific ordering of mailto and https methods is not known to negatively impact email deliverability or result in blocklisting.

Key considerations

• Compliance requirements: Ensure your List-Unsubscribe header meets the requirements for major providers like Gmail and Yahoo, especially for one-click unsubscribe. Learn more about these requirements and their impact on our page about Yahoo and Gmail list-unsubscribe requirements.
• Preference for HTTPS: Given the general preference of email clients for HTTPS, it is often recommended to place the https URL first, though it's not a strict requirement.
• Avoid multiple headers: Do not include multiple List-Unsubscribe headers in a single email, as this can lead to parsing issues and potentially affect deliverability. Our guide on whether List-Unsubscribe header order matters provides further insight.
• Understanding RFC 8058: For a deeper dive into one-click unsubscribe and its technical requirements, it is beneficial to consult the Mailgun blog on RFC 8058.

Key opinions

• User experience focus: Marketers prioritize an easy unsubscribe experience to keep subscribers engaged and minimize frustration, which benefits deliverability.
• Client compatibility: Many advocate for including both mailto and https links to cater to the widest range of email clients, old and new.
• Reputation protection: A clear unsubscribe path helps protect sender reputation by giving recipients an alternative to marking emails as spam, which can lead to being placed on a blocklist.
• Pragmatic approach: While not strictly necessary per spec, some marketers prefer to place the https link first for perceived safety, given its RFC 8058 requirement.

Key considerations

• Preference center integration: Consider how the unsubscribe link integrates with your existing preference center to ensure a smooth user journey. Our article on List-Unsubscribe and preference centers can offer guidance.
• Transactional emails: Even for transactional emails, a properly configured List-Unsubscribe header can positively impact sender reputation. Read about this further in our piece: List-Unsubscribe header reputation.
• Best practices for implementation: It is generally advised to provide both unsubscribe methods for optimal compatibility, as suggested by Postmastery regarding sustained deliverability.

Key opinions

• RFC 8058 dictates: The RFC 8058 standard for one-click unsubscribe explicitly requires an https URI but makes no mention of the order of methods.
• MUA discretion: Email clients (MUAs) determine which unsubscribe method to present or use. For RFC 8058 compliant clients, the https URL is preferred and utilized automatically.
• No order significance: Experts confirm that the placement of mailto before or after https does not affect how major email providers like Google or Yahoo process the unsubscribe request.
• Multiple URLs: While the order of mailto vs. https doesn't matter, having multiple https or mailto URLs within the header is generally discouraged.

Key considerations

• Standard adherence: Ensure your implementation strictly follows RFC 8058 for one-click unsubscribe functionality, focusing on the presence of the https URL. This is crucial for compliance with modern email service provider mandates.
• One-click functionality: The primary goal should be to provide a reliable one-click unsubscribe option. Understanding how these links function is key to effective deliverability.
• Avoiding issues: To prevent unexpected behavior or parsing errors by email clients, avoid sending multiple List-Unsubscribe headers or multiple links of the same type within a single header. Our article on what RFC 5322 says versus works offers relevant context.
• Amazon SES guidance: Amazon SES documentation provides an example where the List-Unsubscribe header is followed by List-Unsubscribe-Post. This order is specifically for the interaction between these two headers, not the internal order of mailto and https within the first header (refer to the AWS SES one-click unsubscribe guide).

Key findings

• RFC 8058 specifies URI types: The RFC states that the List-Unsubscribe header must contain at least one https URI for one-click unsubscribe, but it does not dictate the position relative to mailto URIs.
• Optional mailto: The RFC considers mailto links as optional additions to the header, serving as a legacy or alternative unsubscribe method.
• No preference indicated: The specification implicitly leaves the processing order of multiple URIs to the MUA, with the understanding that https is for automated one-click actions.

Key considerations

• Adhere to the standard: The primary focus should be on fulfilling the mandatory requirements of RFC 8058, especially including a valid https URI. Ensure all parts of your List-Unsubscribe header are compliant.
• Functional priority: While order is not specified, the functional priority for modern email clients is typically the https link, which should be robust and handle immediate unsubscription.
• Best practices for implementation: For specific examples of how to implement one-click unsubscribe in compliance with RFC 8058, Amazon SES documentation provides helpful practical guides, such as their article on using one-click unsubscribe.