From May 5, 2025, Microsoft is strictly enforcing its email sender requirements. This move requires anyone sending over 5,000 emails per day to Outlook.com, Hotmail, and other Microsoft consumer mailboxes to properly authenticate their messages. Failure to do so will no longer result in your emails landing in Junk, they’ll be rejected outright with a “550 5.7.15 Access denied” error.

This applies to emails being sent to Microsoft’s consumer email services — Outlook.com, Hotmail.com, and Live.com.

Key Takeaways

Microsoft will reject emails from high-volume senders (>5,000/day) that lack proper authentication starting May 5, 2025.
Non-compliant emails will trigger the “550 5.7.15 Access denied” rejection error.
To comply, senders must correctly implement SPF, DKIM, and DMARC.
Domain misalignment, or missing authentication records, will cause hard rejections.
PowerDMARC can simplify compliance and ensure your messages reach Microsoft inboxes.

What Microsoft’s New Requirements Mean for Senders

Image source: Microsoft Tech Community

If you’re a high-volume sender, you must act now. Microsoft’s updated enforcement goes beyond simply flagging suspicious emails, it rejects them completely if they lack proper authentication.

While the initial plan was to direct non-compliant messages to recipients’ Junk folders, Microsoft has revised its approach to address potential confusion and enhance security for users. On rejection, the error you’ll encounter looks like this:

550 5.7.15 Access denied, sending domain [SendingDomain] does not meet the required authentication level.

Understanding 550 5.7.15 Access Denied Error Code

The 550 5.7.15 Access denied error is a specific SMTP response from Microsoft that signals a failure in authentication.

Post the May 5th deadline, this can be triggered by:

Lacking email authentication records (SPF, DKIM, DMARC).
Misconfigured or erroneous email authentication records.
Misalignment between the domain used in the “From” header and those used in your SPF and DKIM signatures.
Missing or not enabled DMARC policy.

Microsoft Sender Rules: The Core Requirements

Enable SPF – Sender Policy Framework or SPF verifies IP addresses allowed to send emails on your domain’s behalf. According to Microsoft’s sender rules, SPF must pass for the sending domain.
Implement DKIM – DomainKeys Identified Mail or DKIM helps prevent email tampering by appending digital signatures to outgoing emails. According to Microsoft’s sender rules, DKIM must pass for the sending domain.
Configure DMARC – Domain-based Message Authentication, Reporting & Conformance or DMARC ties it all together by allowing you to take action against unauthorized emails and providing visibility on your email channels. Microsoft recommends DMARC to be configured at least at p=none, with SPF and DKIM aligned, or preferably both.

Additional email hygiene recommendations include using compliant sender addresses, providing functional unsubscribe links, maintaining list hygiene, and ensuring transparent mailing practices to improve deliverability and trust.

Note: PowerDMARC recommends starting DMARC implementation at a “none” policy while monitoring your emails. Following this, slowly shift to enforcement with “quarantine” and then “reject” for protection against email-based cyber attacks.

How to Comply with Microsoft’s Sender Requirements

To avoid rejected emails and ensure seamless delivery:

Set up or correct SPF, DKIM, and DMARC records on your domain.
Make sure domain alignment is properly configured in your email headers.
Make sure SPF and DKIM are passing for your domain.
Ensure your DMARC policy is properly enabled.

Check Your Domain’s Compliance

Why Do It Alone? Let PowerDMARC Help

Use PowerDMARC to simplify setup, monitor authentication status, and enforce policies with ease.

Manually setting up SPF, DKIM, and DMARC can be technically challenging, time-consuming, and error-prone. One misconfigured record, alignment issues, or a missing policy, and your email may be rejected! This may result in lost business opportunities and damaged sender reputation. PowerDMARC simplifies compliance with:

Automated authentication record configuration
Real-time monitoring and insights
Guided policy enforcement
SPF error handling

Start your 15-day free DMARC trial with PowerDMARC today!

Final Thoughts

The May 5, 2025 deadline is fast approaching. If you’re a high-volume sender, inaction means losing access to Microsoft inboxes. Don’t wait for the 550 5.7.15 rejection to hit your logs. Act now by setting up your email authentication today and stay deliverable, trusted, and secure.

About
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Ahona Rudra

Domain & Email Security Expert at PowerDMARC

Ahona is the Marketing Manager at PowerDMARC, with 5+ years of experience in writing about cybersecurity topics, specializing in domain and email security. Ahona holds a post-graduation degree in Journalism and Communications, solidifying her career in the security sector since 2019.

Microsoft Sender Requirements Enforced — How to Avoid 550 5.7.15 Rejections