Does Microsoft support RFC 8058 list-unsubscribe-post?

Key findings

• Confirmed support: Recent tests show that Microsoft Outlook does process the List-Unsubscribe-Post header, enabling one-click unsubscribe functionality.
• Implementation nuances: The POST request from Microsoft might structure parameters differently than some senders expect, often placing the unsubscribe ID directly in the URL query string rather than the request body.
• Unclear UI integration: Unlike Gmail or Yahoo, Microsoft Outlook's user interface may not always prominently display an explicit Unsubscribe button directly in the header, even when RFC 8058 is supported. Learn more about Outlook's List-Unsubscribe options.
• Assumed GET vs POST: If only an HTTP List-Unsubscribe link is provided without List-Unsubscribe-Post, Microsoft might attempt a GET request to the URL, which typically requires a confirmation step, defeating the one-click purpose.

Key considerations

• Full RFC 8058 compliance: To ensure reliable one-click unsubscribes across all major mailbox providers, including Microsoft, senders should fully implement RFC 8058. This includes providing both a List-Unsubscribe header with an HTTP(S) URL and a List-Unsubscribe-Post header. You can review the RFC 8058 documentation.
• Handling POST requests: Your unsubscribe endpoint should be configured to correctly parse the unsubscribe ID from both the URL query string and the request body to accommodate variations in how different email clients send the POST request.
• Testing is key: Regularly test your unsubscribe process, especially with Microsoft Outlook accounts, to ensure that the one-click functionality works as intended. This helps verify compliance and user experience. Suped's email deliverability tester can assist with this.
• Impact on sender reputation: Providing an easy unsubscribe option reduces spam complaints, which is vital for maintaining a positive sender reputation and avoiding blocklists.

Key opinions

• Initial uncertainty: Many marketers initially found Microsoft's support for List-Unsubscribe-Post to be unclear, leading to speculation about its functionality in Outlook.
• Testing confirms support: Through hands-on testing, some marketers have confirmed that Microsoft does indeed process the List-Unsubscribe-Post header.
• Mismatched expectations: Some marketers noted that the format of the POST request from Microsoft might differ from their initial assumptions, specifically regarding how the unsubscribe ID is passed (e.g., in the URL query string rather than the body).
• UI discrepancies: Observations suggest that Microsoft's user interface might not always show a distinct Unsubscribe option directly in the email header like some other providers, even when the underlying support is present. This can lead to confusion for subscribers.

Key considerations

• Adaptation of unsubscribe logic: Marketers should ensure their unsubscribe logic can correctly extract the unsubscribe identifier from various POST request formats, including those where it's part of the URL.
• Unified unsubscribe approach: It is advisable to implement full RFC 8058 compliance to meet the requirements of all major mailbox providers, rather than optimizing for one. This includes having both HTTP and POST List-Unsubscribe headers. For more information, see our guide on one-click unsubscribe requirements for Yahoo and Google.
• Minimizing spam complaints: Providing an easy, one-click unsubscribe option is crucial for reducing user frustration and the likelihood of recipients marking emails as spam, which negatively impacts sender reputation. This is especially true given Microsoft's sender requirements for 2025, even if RFC 8058 is not explicitly mandated yet.
• Proactive testing: Marketers should regularly test their unsubscribe flows across different email clients to ensure compliance and a smooth user experience. This includes testing what happens when a user reports spam.

Key opinions

• Implicit support confirmed: Experts generally agree that despite a lack of explicit, forceful mandates, Microsoft does process RFC 8058 List-Unsubscribe-Post headers for one-click unsubscribes.
• POST body irrelevant: Some experts point out that the body of the POST request from Microsoft's unsubscribe action often contains no useful information and that senders should focus on parsing the unsubscribe identifier from the URL itself.
• Behavior with mixed headers: There are observations that if both HTTP and mailto List-Unsubscribe options are provided, Microsoft might prefer the mailto option, potentially leading to a two-step unsubscribe process for some users. Learn more about mailto links and one-click unsubscribe.
• Importance regardless of mandate: Even without a strict mandate, implementing RFC 8058 is considered a best practice for all senders aiming for high deliverability and good sender reputation, as it minimizes spam complaints.

Key considerations

• Holistic implementation: Experts recommend implementing the full RFC 8058 specification, including both List-Unsubscribe with a URL and List-Unsubscribe-Post, to ensure compatibility across all major mailbox providers, including Microsoft Outlook. This includes understanding how to add an unsubscribe button to the email header.
• Robust unsubscribe handler: The unsubscribe endpoint should be flexible enough to handle various request formats, parsing unsubscribe identifiers whether they come in the POST body or the URL query string. This is key to preventing RFC 8058 failures.
• Monitoring and adaptation: Deliverability experts continually monitor mailbox provider behavior and recommend adapting sending practices to ensure ongoing compliance and optimal performance, especially as requirements evolve.
• Mitigating blocklist risk: An ineffective unsubscribe process can lead to increased spam complaints, contributing to a poor sender reputation and potential inclusion on email blocklists or blacklists. Implementing one-click unsubscribe helps mitigate this risk significantly.

Key findings

• Standard definition: RFC 8058 describes a method for a true one-click unsubscribe via an HTTPS URI POST that should trigger an unsubscribe within 48 hours.
• Header requirement: The standard requires senders to include both a List-Unsubscribe header field and a List-Unsubscribe-Post header field in their messages for one-click functionality. For details on header configuration, see our article on verifying List-Unsubscribe headers.
• Automated unsubscribe: The core purpose of RFC 8058 is to allow subscribers to instantly opt out of mailing lists directly from their email interface, without visiting a web page or sending a separate email.
• Focus on user-friendliness: RFC 8058 aims to make the unsubscribe process easier and more user-friendly by standardizing the one-click method.

Key considerations

• Interoperability: While RFC 8058 provides a clear standard, individual mailbox providers may implement it with slight variations. Senders should ensure their unsubscribe endpoints are robust and can handle different POST request formats (e.g., query string vs. request body).
• Compliance for bulk senders: Even if Microsoft hasn't explicitly made RFC 8058 mandatory for all senders, other major providers like Gmail and Yahoo have. Adhering to this standard ensures broad compliance and improved deliverability across the ecosystem. See Mailgun's guide on RFC 8058.
• Security of unsubscribe links: The RFC specifies using HTTPS for unsubscribe links to ensure secure communication, which is a critical aspect for protecting user data and preventing abuse.
• Avoiding two-step processes: The goal of RFC 8058 is a true one-click unsubscribe. If a sender's setup causes an intermediate confirmation page, it deviates from the standard's intent, potentially frustrating users and increasing spam complaints. We also have a guide on URL compliance with RFC 8058.