Summary
Microsoft's new email sender requirements, effective February 2024, align closely with those introduced by Google and Yahoo, aiming to enhance email security and user experience. These mandates focus on three critical pillars: strong email authentication through SPF, DKIM, and DMARC; maintaining a very low spam complaint rate, ideally below 0.1%; and providing an easy, one-click unsubscribe mechanism for all marketing messages. Enforcement has commenced, with email marketers observing specific bounce messages, such as '550 5.7.515 Access denied,' indicating a failure to meet the required authentication levels. Even with a DMARC 'p=none' policy, messages can be rejected if overall sender reputation is poor, highlighting Microsoft's holistic approach to deliverability beyond just technical compliance.
Key findings
- Core Requirements Mirror Google: Microsoft's new email sender requirements, effective February 2024, largely parallel Google and Yahoo's. They focus on three key areas: strong email authentication (SPF, DKIM, DMARC), maintaining a very low spam complaint rate (ideally below 0.1%), and providing an easy, one-click unsubscribe process for marketing messages.
- Specific Enforcement Bounces: Observed enforcement bounces include the new '550 5.7.515 Access denied, sending domain doesn't meet the required authentication level' message, specifically for authentication failures. Other bounces related to DMARC failure (e.g., '5.7.25') and general rejections ('550 5.7.1') are also occurring, indicating direct enforcement of DMARC policies.
- Authentication is Paramount: Microsoft implicitly and explicitly requires SPF, DKIM, and DMARC configuration for good deliverability. Even if a DMARC policy is set to 'p=none', messages can still bounce if other factors, such as sender reputation, are poor, often detailed in the 'Authentication-Results' header.
- Gradual Enforcement Rollout: Enforcement began gradually in February 2024. Observations include campaigns being partially blocked, where a percentage of emails were rejected for specific reasons while others were allowed through, suggesting a phased approach to full compliance enforcement.
- Sender Reputation is Key: Microsoft places significant emphasis on sender reputation, which is built through consistent low spam complaint rates, good sending practices, and engagement metrics. Failure to meet these behavioral criteria, even with technical authentication in place, can lead to deliverability issues and bounces.
Key considerations
- Proactive Implementation: All senders, particularly bulk emailers, must immediately implement SPF, DKIM, and DMARC. While DMARC with a 'p=none' policy is a starting point, 'p=quarantine' or 'p=reject' are considered best practices for enhanced security and deliverability. Valid reverse DNS (PTR records) for sending IPs are also essential for robust sender reputation with Microsoft.
- Monitor Bounce Codes: Actively monitor and understand Microsoft's specific bounce messages. The new '550 5.7.515 Access denied' bounce explicitly indicates a failure to meet required authentication levels. Other relevant codes include '550 5.7.1' for blocked senders or DMARC policy rejections, and '5.7.25' for DMARC validation failures, even for domains with a 'p=reject' policy. Observing these bounces helps diagnose and resolve compliance issues quickly.
- Maintain Low Complaint Rates: Strive to keep spam complaint rates consistently below 0.1%. This requires active list management, sending relevant content, and removing inactive or disengaged subscribers. High complaint rates, even with DMARC in place, can lead to messages being rejected, quarantined, or IPs being blocked by Microsoft's SmartScreen filter.
- Implement One-Click Unsubscribe: For marketing and bulk messages, ensure the one-click unsubscribe mechanism is correctly implemented in your email headers. This requirement improves user experience and is a critical factor Microsoft tracks for compliance, influencing your sender reputation and deliverability.
- Holistic Sender Behavior: Beyond technical authentication, Microsoft evaluates overall 'good sender behavior.' This includes promptly processing unsubscribe requests, maintaining clean email lists to prevent bounces, ensuring consistent sending volume, and avoiding practices that lead to poor engagement. Microsoft is aggressive in blocking senders with poor engagement or high complaint rates, even if DMARC is set to 'p=none'.
What email marketers say
14 marketer opinions
The new email sender requirements from Microsoft have initiated a significant shift in deliverability expectations, with enforcement beginning in February 2024. These mandates largely parallel Google and Yahoo's recent updates, focusing on three core areas: robust email authentication via SPF, DKIM, and DMARC; a stringent cap on spam complaint rates, ideally below 0.1%; and the provision of a straightforward one-click unsubscribe mechanism for all bulk mail. Marketers are now encountering specific bounce messages, such as the distinct '550 5.7.515 Access denied' error, signaling a failure to meet the required authentication levels. Furthermore, Microsoft's enforcement extends beyond mere technical compliance; a sender's overall reputation, shaped by factors such as low complaint rates, good engagement, and consistent sending practices, profoundly influences deliverability, with poor behavior leading to rejections even if basic DMARC is in place.
Key opinions
- Core Requirements Confirmed: Microsoft's 2024 requirements align with Google and Yahoo, mandating SPF, DKIM, DMARC, a spam complaint rate under 0.1%, and one-click unsubscribe for bulk senders.
- New Authentication Bounce: A specific bounce message, '550 5.7.515 Access denied, sending domain doesn't meet the required authentication level,' indicates non-compliance with Microsoft's authentication standards. This differs from standard DMARC reject bounces.
- DMARC Enforcement Varied: While DMARC is required, observed bounces include DMARC verification failures, for example, for domains missing SPF or DKIM, and rejections can occur even with a 'p=none' policy if sender reputation is poor.
- Phased Enforcement Observed: Enforcement began gradually, with some campaigns experiencing partial blocking, where a percentage of emails were rejected for specific reasons while others were delivered, suggesting a measured rollout.
- Sender Reputation is Crucial: Microsoft emphasizes overall sender reputation, tracking metrics like consistent low spam complaint rates and good sending practices, which can lead to deliverability issues and blocks even if technical authentication is present.
Key considerations
- Implement Full Authentication: All senders must ensure SPF, DKIM, and DMARC are properly configured. While a DMARC 'p=none' policy may suffice initially, adopting 'p=quarantine' or 'p=reject' is recommended for stronger protection and improved deliverability.
- Monitor Specific Bounce Codes: Pay close attention to new Microsoft bounce messages, particularly the '550 5.7.515 Access denied' code, which directly signals authentication-level non-compliance, aiding in prompt issue resolution.
- Prioritize Low Spam Rates: Actively manage email lists and content to maintain spam complaint rates consistently below the 0.1% threshold, as high complaints are a significant factor in Microsoft's SmartScreen filtering and lead to rejections.
- Enable One-Click Unsubscribe: For all marketing and bulk email, correctly implement the List-Unsubscribe and List-Unsubscribe-Post headers to provide a seamless one-click unsubscribe experience, a critical compliance factor.
- Foster Good Sender Behavior: Beyond technical checks, focus on holistic sender practices, including timely unsubscribe processing, regular list hygiene to prevent bounces, and consistent sending volume, as these behaviors are crucial for building and maintaining a positive sender reputation with Microsoft.
Marketer view
Email marketer from Email Geeks explains that Microsoft's email sender requirements enforcement has begun and shares a link to Microsoft's Sender Requirements Update Announcement.
27 Aug 2021 - Email Geeks
Marketer view
Email marketer from Email Geeks shares observing the first non-compliance bounces, initially a DMARC verification failure for domains without SPF or DKIM, and later confirming the new "550 5.7.515 Access denied" bounce related to Microsoft's required authentication level.
18 Sep 2021 - Email Geeks
What the experts say
3 expert opinions
Microsoft's new email sender requirements, which took effect in February 2024, closely mirror those implemented by Google and Yahoo, emphasizing enhanced email security and a better user experience. These mandates center on three crucial areas: robust email authentication (SPF, DKIM, DMARC), maintaining a low spam complaint rate (specified as below 0.3% by some experts), and providing a simple one-click unsubscribe mechanism for bulk mail. Enforcement is actively underway, with observed bounce codes, such as 5.7.25, specifically indicating rejections for messages that fail DMARC validation, especially when the sending domain has a 'p=reject' policy. This active enforcement directly impacts mail sent to Outlook and Hotmail users, underscoring the necessity of strict compliance.
Key opinions
- Aligned Core Requirements: Microsoft's new email sender requirements, effective February 2024, closely parallel Google's and Yahoo's, focusing on strong authentication (SPF, DKIM, DMARC), a low spam complaint rate (under 0.3%), and a one-click unsubscribe mechanism.
- Specific DMARC Enforcement: Microsoft has commenced direct enforcement of DMARC policies, leading to observed bounces with a '5.7.25' error code for emails that fail DMARC validation, especially when the sending domain has a 'p=reject' policy.
- Direct Service Impact: The DMARC enforcement and associated bounce codes specifically impact email deliverability to Outlook and Hotmail users, signifying active compliance checks for these services.
Key considerations
- Ensure DMARC Validation: Given Microsoft's active enforcement of DMARC policies, particularly for domains with a 'p=reject' setting, senders must ensure their mail consistently passes DMARC validation to prevent rejections, indicated by the '5.7.25' error code.
- Target Low Complaint Rates: Strive to maintain a spam complaint rate below 0.3%, as this threshold is a key component of Microsoft's new requirements and directly impacts deliverability.
- Implement One-Click Unsubscribe: For all bulk email, correctly implement a one-click unsubscribe mechanism, as this is a mandatory requirement for improving user experience and maintaining good sender standing with Microsoft.
Expert view
Expert from Spam Resource explains that Microsoft's new email sender requirements, effective February 2024, parallel Google's, focusing on three key areas: message authentication (SPF, DKIM, DMARC), one-click unsubscribe, and maintaining a low spam complaint rate.
13 Jun 2023 - Spam Resource
Expert view
Expert from Spam Resource shares that Microsoft has begun enforcing DMARC policies for some senders, specifically observing bounces with a 5.7.25 error code for mail that fails DMARC validation when the sending domain has a p=reject policy. This enforcement impacts mail sent directly to Outlook and Hotmail users.
25 Sep 2022 - Spam Resource
What the documentation says
6 technical articles
Building on prior announcements, Microsoft's comprehensive email sender requirements, implemented in February 2024, are designed to enhance security and user experience. These mandates reinforce the critical need for strong email authentication using SPF, DKIM, and DMARC, alongside maintaining an exceptionally low spam complaint rate and offering a straightforward one-click unsubscribe option for marketing communications. Crucially, Microsoft Exchange Online Protection (EOP) rigorously assesses senders based on a combination of these technical checks, overall sender reputation, and content analysis. Non-compliance, especially with the 2024 updates, directly leads to message rejection or quarantine, frequently observed through specific enforcement bounces like 550 5.7.1, signaling blocked senders or DMARC policy violations. The importance of a valid reverse DNS (PTR record) for sending IPs is also highlighted as a component of robust sender reputation.
Key findings
- Core Requirements Reinforced: Microsoft's February 2024 requirements emphasize robust email authentication (SPF, DKIM, DMARC), a very low spam complaint rate, and easy one-click unsubscribe for marketing messages, aligning with previous communications.
- Authentication Prerequisite: Exchange Online Protection (EOP) strongly recommends and implicitly requires SPF, DKIM, and DMARC to prevent spoofing and phishing, essential for meeting new deliverability standards.
- Sender Reputation & RDNS: Meeting deliverability criteria also necessitates a strong sender reputation, which includes maintaining a valid reverse DNS (PTR record) for sending IPs alongside proper SPF, DKIM, and DMARC configurations.
- Specific Rejection Codes: Enforcement failures manifest as non-delivery reports (NDRs), such as 550 5.7.1, which can indicate blocked senders or messages rejected due to DMARC policy non-compliance.
- EOP's Holistic Filtering: Exchange Online Protection determines spam through a combination of sender reputation, content analysis, and strict authentication checks, with failure to meet these criteria leading to message rejections.
Key considerations
- Complete Authentication: Fully implement and verify SPF, DKIM, and DMARC records to meet Microsoft's implicit and explicit authentication requirements and prevent spoofing.
- Valid Reverse DNS: Ensure all sending IP addresses have properly configured reverse DNS (PTR records), as this is a crucial element for building and maintaining a strong sender reputation with Microsoft.
- Monitor NDR Codes: Proactively monitor for and interpret specific non-delivery report (NDR) codes, such as 550 5.7.1, to promptly identify and address issues related to blocked senders or DMARC policy rejections.
- Maintain Low Complaints: Actively manage email lists and content to maintain a very low spam complaint rate, which is a core component of Microsoft's sender evaluation and directly impacts deliverability.
- Implement 1-Click Unsubscribe: For all marketing and bulk email, ensure an easily accessible, one-click unsubscribe mechanism is in place, as this is a mandatory requirement for compliance and improved user experience.
- Understand EOP Assessment: Understand that Exchange Online Protection (EOP) uses a multi-faceted approach, combining authentication checks, sender reputation, and content analysis, to determine email legitimacy and deliverability.
Technical article
Documentation from Microsoft Tech Community explains that new email sender requirements for Microsoft recipients, effective February 2024, focus on three key areas: strong email authentication (SPF, DKIM, DMARC), a very low spam complaint rate, and an easy, one-click unsubscribe process for marketing messages.
17 Dec 2023 - Microsoft Tech Community
Technical article
Documentation from Microsoft Learn explains that for email authentication in Exchange Online Protection (EOP), Microsoft strongly recommends and implicitly requires the configuration of SPF, DKIM, and DMARC to help prevent spoofing and phishing, which are critical for good deliverability under the new sender policies.
27 Apr 2024 - Microsoft Learn
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