Summary
Emails initiated via mailto: unsubscribe links from Laposte.net users frequently fail DMARC authentication because they bypass the domain's official, DMARC-compliant sending infrastructure. When a user's local email client sends such an email, the sending IP address typically does not align with Laposte.net's published SPF records, and the email lacks a valid DKIM signature from the Laposte.net domain. As DMARC requires either SPF or DKIM alignment with the From header domain to pass authentication, these client-sent messages are flagged as unauthenticated, especially when the sender's DMARC policy is set to quarantine or reject.
Key findings
- Client-Sent Unsubscribes: Emails generated by mailto: links are sent directly from the user's local email client, bypassing Laposte.net's controlled and DMARC-configured mail servers.
- SPF Alignment Failure: The sending IP address of the user's client-generated email does not match the authorized IP ranges listed in Laposte.net's SPF record, causing SPF authentication failure.
- Missing DKIM Signature: User-initiated emails through mailto: links are not signed with Laposte.net's private DKIM key, resulting in a lack of DKIM authentication alignment.
- DMARC Policy Enforcement: Because both SPF and DKIM authentication fail to align with the From domain (laposte.net), DMARC policies, such as a quarantine setting, are enforced by receiving mail servers, leading to authentication failures.
- Legal Obligation to Honor: Despite the DMARC authentication failures, there remains a legal requirement for recipients to honor these unsubscribe requests.
Key considerations
- Unreliable Unsubscribe Method: Mailto: unsubscribe links are generally unreliable for ensuring proper email deliverability and DMARC compliance due to their client-side initiation.
- Alternative Unsubscribe Options: Implementing more robust unsubscribe methods, such as a List-Unsubscribe header or a dedicated web-based unsubscribe form, is recommended for better deliverability and user experience.
- Third-Party Sender SPF Check: In specific cases, third-party services like Vade (or vaderetro-safeunsubscribe.com) may be involved, and their sending IPs or domains must be properly included in the domain owner's SPF records if they are sending on behalf of that domain.
- Recipient-Side Handling: Some recipient systems may use special MX records for unsubscribe emails or might not check DMARC on these specific messages, though this is a recipient-side mitigation, not a sender-side solution.
What email marketers say
12 marketer opinions
The fundamental reason mailto: unsubscribe emails from Laposte.net fail DMARC authentication stems from their nature as client-generated messages. When a user initiates an email via a mailto: link, their personal email client or local ISP's SMTP server sends the message, effectively bypassing Laposte.net's official, DMARC-compliant email infrastructure. Consequently, these emails typically lack the necessary SPF alignment-the sending IP does not match Laposte.net's authorized senders-and they do not carry a valid DKIM signature from the Laposte.net domain. Because DMARC mandates either SPF or DKIM alignment with the From header domain to pass authentication, these non-aligned messages are flagged as unauthenticated, especially problematic when Laposte.net's DMARC policy is set to quarantine. This highlights a broader issue: DMARC is designed to prevent spoofing by requiring authenticated sending sources, and mailto: links inadvertently trigger failures by circumventing standard, controlled sending pathways.
Key opinions
- Client-Initiated Sending: Emails generated by mailto: links originate directly from the end-user's local email client or ISP's server, not from Laposte.net's controlled email infrastructure.
- Authentication Misalignment: These client-sent messages typically fail DMARC because their sending IP does not align with Laposte.net's SPF records, and they lack a valid DKIM signature from the domain.
- Third-Party SPF Gaps: Specific third-party services, such as Vade's IP 185.187.30.19 or the Return-Path domain vaderetro-safeunsubscribe.com, have been identified as lacking proper SPF records, contributing to authentication failures when involved in the sending path.
- DMARC's Purpose: DMARC's core function is to ensure the From domain is authenticated by SPF or DKIM to prevent spoofing, a standard that client-generated emails from mailto: links often cannot meet.
- Recipient-Side Nuances: Some recipient systems may handle these unsubscribe emails via special MX records or might not check DMARC on them, considering a mass unsubscribe spoofing attack an unlikely threat vector.
Key considerations
- Unreliability of Mailto: Mailto: unsubscribe links are generally unreliable for ensuring successful email deliverability and DMARC compliance due to their uncontrolled, client-side initiation.
- Legal Obligation: Despite DMARC authentication failures, email marketers are legally obligated to honor unsubscribe requests, underscoring the need to process these messages even if flagged.
- Infrastructure Importance: For domains with strong DMARC policies, it is crucial that all email, including unsubscribe requests, originates from properly authenticated and aligned sending infrastructure.
- Alternative Unsubscribe Methods: Implementing more robust and DMARC-compliant unsubscribe mechanisms, such as a List-Unsubscribe header or a web-based unsubscribe form, is highly recommended.
Marketer view
Email marketer from Email Geeks explains that mailto: unsubs received from laposte.net are failing authentication due to Vade's IP 185.187.30.19 not being included in their SPF, and laposte.net's DMARC being set to quarantine. He notes the absence of DKIM and the legal requirement to honor these unsubscriptions despite the authentication failures.
6 Jan 2025 - Email Geeks
Marketer view
Email marketer from Email Geeks notes that the Return-Path domain for the failing emails, vaderetro-safeunsubscribe.com, has no SPF record. He also states that their system does not check DMARC on these specific unsubscribe emails because they are sent to a special MX, and considers the idea of a mass unsubscribe spoofing attack to be a largely useless vector.
17 Dec 2024 - Email Geeks
What the experts say
1 expert opinions
When a user initiates an unsubscribe request via a mailto: link, the email is sent directly from their personal email client or local ISP, rather than through Laposte.net's official email infrastructure. DMARC (Domain-based Message Authentication, Reporting & Conformance) is an email authentication protocol that validates the domain in an email's 'From' header against its actual sending source. If the unsubscribe email's 'From' address is, for example, 'user@laposte.net', DMARC authentication is applied to the 'laposte.net' domain. The failure occurs because the user's client is not an authorized sending source for Laposte.net, leading to a lack of SPF alignment or a valid DKIM signature from Laposte.net. This highlights that while Laposte.net is the recipient of the unsubscribe request, the DMARC failure pertains to the authentication of the incoming email's origin, not Laposte.net's own outbound email policies.
Key opinions
- DMARC Authenticates From Domain: DMARC's primary function is to verify the domain specified in an email's 'From' header by checking its alignment with SPF or DKIM.
- Client-Initiated Sending: Emails generated via mailto: links are sent directly from the end-user's local email client or ISP's SMTP server, bypassing the official email infrastructure of the 'From' domain.
- Authentication Mismatch: If the 'From' domain of the unsubscribe email is, for instance, 'laposte.net', DMARC authentication for 'laposte.net' will fail because the user's client's sending IP is not listed in Laposte.net's SPF records, nor does the email carry a valid DKIM signature from Laposte.net.
- Laposte.net as Recipient: In the context of these unsubscribe emails, Laposte.net is the intended recipient, meaning the DMARC failure relates to the inbound message's authentication, not Laposte.net's own outbound email deliverability or DMARC policy for emails they send.
Key considerations
- DMARC's Application Scope: It is crucial to distinguish that DMARC applies to the domain in the 'From' header of an email and its actual sending source, not to the domain that is merely receiving the email.
- Unreliability of Mailto Links: Mailto: links are inherently unreliable for ensuring DMARC compliance because the sending process is outside the control of the domain owner and their authenticated infrastructure.
- Robust Unsubscribe Alternatives: To ensure deliverability and proper authentication for unsubscribe requests, it is advisable to implement more controlled methods such as a List-Unsubscribe header or a dedicated web-based unsubscribe form.
Expert view
Expert from Word to the Wise explains that DMARC (Domain-based Message Authentication, Reporting & Conformance) is an email authentication protocol that tells receiving mail servers whether or not a message from a specific domain is actually from that domain. This means DMARC applies to the *sending domain* of an email. Therefore, if a user sends an email via a mailto: link for an unsubscribe request, DMARC authentication would apply to the user's sending domain, not to Laposte.net, as Laposte.net is the recipient and not the sender of that email initiated by the mailto: link.
9 Nov 2023 - Word to the Wise
What the documentation says
5 technical articles
Mailto: unsubscribe emails from Laposte.net consistently fail DMARC authentication because their method of transmission inherently conflicts with DMARC's core requirements. When a user sends such an email via their local client, it originates from an IP address not authorized in Laposte.net's SPF records, nor does it carry a valid DKIM signature from the Laposte.net domain. Since DMARC relies on either SPF or DKIM alignment with the 'From' domain, these client-initiated messages are deemed unauthenticated. This outcome aligns with DMARC's design to prevent email spoofing by ensuring messages claiming to be from a domain are sent through its authenticated infrastructure.
Key findings
- Local Client Origin: Emails initiated via mailto: links are sent directly from the end-user's local email client or personal ISP's mail server, rather than the official mail infrastructure of the 'From' domain.
- SPF Alignment Deficiency: The sending IP address of these client-generated messages does not match the IP ranges authorized within the 'From' domain's SPF record, causing SPF authentication to fail.
- Missing DKIM Signature: These user-sent emails lack a cryptographically valid DKIM signature applied by the legitimate 'From' domain's mail servers, resulting in a DKIM authentication failure.
- DMARC Core Requirement: DMARC mandates that for an email to pass authentication, the 'From' header domain must align with either the domain validated by SPF or the domain signed by DKIM.
- Impact on From Domain: The failure specifically impacts the 'From' domain (e.g., laposte.net) as the email appears to be an unauthorized attempt to send from that domain, aligning with DMARC's anti-spoofing goals.
Key considerations
- Uncontrolled Sending: Utilizing mailto: links for unsubscribe requests creates an uncontrolled email sending pathway, making it impossible for the domain owner to ensure DMARC compliance.
- Importance of Authorized Infrastructure: For domains enforcing strong DMARC policies, all emails appearing to originate from that domain, including unsubscribe requests, must pass through properly authenticated and aligned sending infrastructure.
- DMARC's Protective Role: The DMARC failure mechanism serves its intended purpose of preventing email spoofing by flagging messages that claim to be from a domain but are not sent via its authorized systems.
- Reliable Unsubscribe Alternatives: To guarantee deliverability and proper authentication for unsubscribe requests, email marketers should implement more secure methods like a List-Unsubscribe header or a dedicated web-based unsubscribe form.
Technical article
Documentation from DMARC.org explains that DMARC authentication requires either SPF or DKIM to align with the From domain in the email header. Emails initiated via mailto: links are sent from the user's local email client, not the authorized mail servers of laposte.net. This means the sending IP address will not match laposte.net's SPF record, and the email will not be signed with laposte.net's DKIM key, causing DMARC alignment to fail.
10 Sep 2024 - DMARC.org
Technical article
Documentation from IETF (RFC 7489, the DMARC specification) clarifies that DMARC relies on the authentication of the organizational domain found in the From header. For SPF, the Return-Path domain must align with the From domain, and the sending IP must be authorized. For DKIM, the d= tag in the signature must align. Emails sent by a laposte.net user via a mailto: link from their local client will typically fail these alignment checks against laposte.net's published records, as they are not sent through laposte.net's official, DMARC-compliant outbound infrastructure.
22 Jun 2021 - RFC-Editor.org
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