Why Your Email Was Rejected by Outlook: Understanding Error 550; 5.7.515 and How to Fix It

Freddie Leeman -

Starting May 5th, 2025, Microsoft Outlook.com will enforce new authentication rules for domains that send more than 5,000 emails per day. If you’re a bulk sender and found your messages rejected with the error:

550; 5.7.515 Access denied, sending domain [example.com] does not meet the required authentication level.

—you’ve run into Microsoft’s tightened authentication policy for high-volume email.

What Does This Error Mean?

The 550; 5.7.515 Access denied rejection means Outlook has outright blocked your message, not just moved it to Junk. This happens when your domain doesn’t meet minimum authentication requirements now enforced for large senders.

Why Is Outlook Doing This?

To strengthen inbox security, reduce spoofing/phishing, and improve trust in email, Outlook now requires all high-volume senders to implement:

  • ✅ SPF: Must pass
  • ✅ DKIM: Must pass
  • ✅ DMARC: Must be present and must align with either SPF or DKIM.

These are not suggestions anymore—they are enforced requirements.

Common Reasons for the 550; 5.7.515 Access denied Error

  1. SPF fails: The sending server’s IP is not listed in the SPF DNS record.
  2. DKIM fails: Your messages aren’t being signed correctly or your DNS is missing a valid public key.
  3. DMARC fails: No policy, misaligned identity, or syntax errors in your DMARC DNS record.
  4. No alignment: The “From” domain doesn’t align with the domain used in SPF or DKIM checks.

How to Fix It

To diagnose and resolve the 550; 5.7.515 error, we recommend starting with our LearnDMARC.com service— a free tool that helps you understand exactly how your emails are authenticated.

Just send an email to the address the site provides, and the tool will visualize the full communication between mail servers, showing whether SPF, DKIM, and DMARC passed or failed. You’ll get a clear, easy-to-read summary of:

  • Whether SPF passed and which IP was evaluated
  • If DKIM was valid and which domain signed the message
  • How DMARC performed and whether alignment was achieved

This is especially useful for catching configuration errors and seeing whether your records are doing what you expect.

Fix Requirements Recap

After reviewing your test results on LearnDMARC.com, here’s what you need to ensure:

  1. SPF Must Pass
    • Your domain's SPF DNS record must include all servers that send mail on your behalf.
    • Example:
      v=spf1 include:yourmailvendor.com ~all
    • Be careful not to exceed the 10 DNS lookup limit.
  2. DKIM Must Pass
    • Email must be cryptographically signed with DKIM.
    • The public DKIM key must be published in your DNS under a valid selector.
  3. DMARC Policy Must Be Present
    • At a minimum:
      v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com
    • Eventually, consider moving to p=quarantine or p=reject once you're confident all sources are authenticating properly.
  4. SPF or DKIM Must Align
    • The domain used in SPF or DKIM must match (or be a subdomain of) the “From” address in the email.
    • Either SPF or DKIM alignment is required.

By using LearnDMARC.com and ensuring all three protocols are configured correctly and in alignment, you’ll be fully compliant with Outlook’s new sending requirements—and avoid this rejection error entirely.

More Sender Requirements & Best Practices

Outlook’s enforcement isn’t happening in isolation—Google and Yahoo have introduced stricter email authentication standards starting in 2024.

Whether you send newsletters, transactional emails, or one-to-one messages, adopting SPF, DKIM, and DMARC is no longer optional—it’s critical for ensuring inbox delivery and protecting your domain from abuse.

To stay ahead:

Final Thought

Outlook’s move isn’t just a policy update—it’s a signal to the entire industry. Email authentication is no longer optional. Fixing these issues won’t just resolve delivery problems—it will also enhance your brand reputation, improve inbox placement, and protect your domain from abuse.

If you’re sending more than 5,000 messages a day, it’s time to act—the junk folder is no longer the worst-case scenario.