Why are mailto: unsubscribe emails from Laposte.net failing DMARC authentication?
Michael Ko
Co-founder & CEO, Suped
Published 30 Jul 2025
Updated 19 Aug 2025
8 min read
Encountering email authentication failures can be incredibly frustrating, especially when they involve critical communications like unsubscribe requests. Recently, we observed a peculiar issue where Laposte.net mailto: unsubscribe emails were failing DMARC authentication. This isn't just a minor glitch, it directly impacts compliance with unsubscribe mandates and user experience.
DMARC, or Domain-based Message Authentication, Reporting, and Conformance, is a crucial email authentication protocol designed to protect domains from spoofing and phishing attacks. It builds upon SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) by providing instructions to receiving mail servers on how to handle emails that fail authentication checks. For DMARC to pass, either SPF or DKIM must align with the From: header domain.
When a DMARC failure occurs, it indicates that the email did not originate from an authorized sender for the domain it claims to be from. This article will delve into the specific scenario with Laposte.net unsubscribe emails, explore the technical reasons behind such DMARC failures, and offer actionable insights for troubleshooting and prevention.
A fundamental aspect of email security is ensuring that all parts of your email's journey pass authentication. While SPF and DKIM perform individual checks, DMARC brings them together, enforcing policies based on their alignment. Alignment refers to whether the domain used in the SPF check (the Return-Path or Mail From) and the domain used in the DKIM signature (the d= tag) match the domain in the visible From: header. When DMARC fails, it often means there's an issue with why DMARC fails even if SPF and DKIM pass because the domains aren't aligning correctly.
This alignment is crucial, especially when third-party services are involved in sending emails on your behalf. If the third-party sender's domain or IP address isn't properly authorized in your domain's SPF record, or if their DKIM signature doesn't align with your From: domain, DMARC will fail. This is a common reason why DMARC, SPF, and DKIM alignment failures can lead to emails landing in spam or being rejected outright.
Dissecting the Laposte.net mailto: unsubscribe issue
The specific issue with Laposte.net's mailto: unsubscribe emails failing DMARC authentication can be attributed to a common scenario involving third-party sending. In this case, Vade Secure, an email security provider, was processing these unsubscribe requests. The email headers revealed that the mail originated from smtp01.vaderetro-safeunsubscribe.com (IP 185.187.30.19) with the From: address appearing as *****@laposte.net.
The primary cause of the DMARC failure was a misconfiguration in Laposte.net's SPF record. The IP address 185.187.30.19, belonging to Vade Secure, was not included in Laposte.net's SPF record. This means that when a receiving server performed an SPF check, it determined that the mail was not authorized to send on behalf of Laposte.net from that IP. Since SPF failed to authenticate, and likely did not align with the From: domain, the DMARC check subsequently failed.
Further complicating the matter, the Return-Path for these emails was unsubscribe@vaderetro-safeunsubscribe.com. It was also noted that vaderetro-safeunsubscribe.com itself did not have an SPF record. This means that even if Vade Secure was somehow authorized by Laposte's SPF record (which it wasn't), the SPF alignment would still fail because the Return-Path domain did not match the From: domain of laposte.net. DMARC requires this alignment (either SPF or DKIM) to pass.
The final piece of the puzzle is Laposte.net's DMARC policy, which was set to p=quarantine. This policy instructs receiving mail servers to treat emails that fail DMARC as suspicious, typically by moving them to the spam folder or holding them in a quarantine. This explains why these legitimate unsubscribe requests were being junked, creating a significant compliance and operational challenge.
Troubleshooting and resolving DMARC authentication issues
Resolving DMARC authentication issues, particularly those involving third-party senders and unsubscribe emails, requires a systematic approach. The first step is always to verify your SPF and DKIM records, ensuring they correctly authorize all legitimate sending sources, including any third-party providers like Vade Secure in this case. Check that the IP addresses of your senders are explicitly included in your SPF record, or that you have include: mechanisms for their respective domains. Simultaneously, verify that DKIM signatures are present and valid, aligning with your From: domain. For a comprehensive overview, consult email authentication facts versus fiction.
Another crucial step is to analyze your DMARC reports. These XML reports provide valuable insights into your email authentication performance, detailing which emails are passing or failing DMARC, and why. By regularly monitoring these reports, you can quickly identify unauthorized sending sources or misconfigurations. You can also gain an understanding on why legitimate email fails DMARC. For Laposte.net's situation, they would need to work with Vade Secure to ensure that the emails sent by Vade on their behalf are properly authenticated and aligned with the laposte.net domain, or at least that the Return-Path domain (vaderetro-safeunsubscribe.com) has its own valid SPF record that authorizes Vade Secure's IPs.
For specific remedies regarding DMARC failures, resources like how to fix the DMARC fail error can provide practical guidance. Implementing a robust DMARC monitoring solution can help track authentication performance and detect issues proactively. Regularly reviewing your list of DMARC tags and their meanings can also aid in policy adjustments as needed. For new DMARC implementations or policy changes, it is always recommended to start with a p=none policy and gradually transitioning your DMARC policy to quarantine or reject as you gain confidence in your authentication setup.
Recommended SPF record structure
Ensuring your SPF record is correctly structured and includes all necessary sending sources is paramount for DMARC alignment. A common mistake is forgetting to add third-party email service providers. Remember, SPF records should not exceed a 10-lookup limit.
The broader implications of unsubscribe DMARC failures
The situation with Laposte.net highlights the critical nature of DMARC compliance, especially for transactional emails like unsubscribe requests. Beyond general deliverability, there are legal requirements in many regions (like GDPR and CAN-SPAM) to honor unsubscribe requests promptly. When these emails fail DMARC and are consequently junked or blocked, organizations face legal risks and damage to their sender reputation. If emails going to spam is a recurring issue, it's vital to address these underlying authentication failures.
Furthermore, such incidents underscore the importance of understanding the intricate relationship between SPF, DKIM, and DMARC. A misstep in one area, such as an incomplete SPF record for a third-party sender, can cascade into DMARC failures and unintended consequences like legitimate mail being treated as spam or blocked (also known as a blacklist or blocklist event). For a more general understanding of these protocols, refer to a simple guide to DMARC, SPF, and DKIM. It also highlights the need for robust an in-depth guide to email blocklists to mitigate impact from unexpected issues.
Sender responsibility
Ensuring all authorized sending IPs and domains are listed in your SPF records and that DKIM is correctly configured and aligned is the sender's fundamental responsibility. This applies to both direct sending and sending through third-party services.
Compliance and reputation
Failing to properly authenticate transactional emails, such as unsubscribe requests, can lead to severe deliverability issues and potential legal repercussions related to email marketing laws.
Receiver interpretation
Receiving mail servers follow the DMARC policy set by the sending domain. If a legitimate email fails authentication and the policy is p=quarantine or p=reject, the email will be treated accordingly, regardless of its legitimate purpose.
Third-party vendor role
Collaboration with third-party email service providers is essential. They must ensure their infrastructure is correctly configured for DMARC alignment and provide clear guidance on necessary DNS record updates.
Views from the trenches
Best practices
Always include all legitimate sending IPs and 'include' mechanisms for third-party senders in your SPF record.
Ensure your DKIM records are correctly published and that the 'd=' domain aligns with your 'From:' header.
Start with a DMARC 'p=none' policy to gather data, then gradually move to 'quarantine' or 'reject' policies.
Regularly monitor your DMARC reports to identify authentication failures and legitimate sources.
Common pitfalls
Forgetting to update SPF records when adding new sending services or IPs, leading to DMARC failures.
Not configuring DKIM correctly, or signing domains that do not align with the visible 'From:' address.
Moving directly to a 'p=reject' DMARC policy without sufficient monitoring, blocking legitimate emails.
Ignoring DMARC failure reports, allowing authentication issues to persist and impact deliverability.
Expert tips
Use a DMARC monitoring platform to automate report analysis and gain actionable insights.
Communicate clearly with third-party vendors about your DMARC requirements and ensure their systems comply.
Implement a consistent 'From:' domain across all your email sending to simplify DMARC alignment.
Be aware of local and international legal requirements for handling unsubscribe requests.
Marketer view
A marketer from Email Geeks reported that mailto: unsubscribe emails from Laposte.net were failing DMARC authentication because Vade's IP was not in Laposte's SPF, and Laposte's DMARC policy was set to quarantine.
2019-04-28 - Email Geeks
Expert view
An expert from Email Geeks suggested examining the Return-Path header and DKIM signature to fully diagnose the DMARC failure.
2019-04-28 - Email Geeks
Key takeaways
The case of Laposte.net's mailto: unsubscribe emails failing DMARC authentication serves as a stark reminder of the complexities of email deliverability, especially when third-party services are involved. DMARC failures most often stem from SPF or DKIM alignment issues, where the sending domain or IP is not properly authorized to send on behalf of the From: domain. This can lead to legitimate emails being quarantined or rejected, impacting essential services like unsubscribe requests.
Proactive DMARC monitoring, meticulous SPF and DKIM configuration, and effective communication with all email service providers are paramount. By taking these steps, organizations can ensure their emails reach their intended recipients, maintain a strong sender reputation, and remain compliant with regulations, avoiding frustrating and potentially costly deliverability challenges.
