What Microsoft’s ‘550; 5.7.515’ error really means (and how to fix it)

You wrote the perfect email. Hit “send.” And then, bam, your message bounces back with a cryptic error: “550 5.7.515 Access denied, sending domain not authorized.”

If you’re staring at that line wondering what it even means (and why Microsoft is blocking your perfectly legit email), you’re not alone. This error has become a common headache for IT teams, marketers, and email admins.

The 550 5.7.515 error isn’t random. It’s Microsoft’s way of saying, “Hey, your email didn’t pass our trust check.” It’s a sign that your domain isn’t playing nice with email authentication protocols like SPF, DKIM, and DMARC.

Below, we’ll break down exactly what this error means, why it’s happening, and how to fix it so your messages land in the inbox (where they belong).

What does Microsoft’s 550; 5.7.515 error mean?

Here’s the message you’re probably seeing in your bounce-back message:

“550 5.7.515 Access denied, sending domain not authorized. Please verify that your email is sent from an authorized sending host and that it aligns with the domain’s authentication policies.”

This means Microsoft rejected your email because it didn’t pass authentication checks. That’s usually due to one of the following:

• The sending server isn’t authorized to send on behalf of your domain.
• Your email fails DMARC alignment.
• Your domain’s SPF or DKIM records are missing, misconfigured, or incomplete.

It’s part of Microsoft’s changing sender requirements that are designed to reduce phishing.

Unfortunately, even if you are a legitimate sender, if your domain’s authentication setup isn’t rock-solid, Microsoft will still block you. It’s all about trust. And trust in the email world comes from properly configured DNS records (like DMARC, SPF, and DKIM). 

So while the error feels frustrating, it’s really a sign that something in your email authentication setup needs attention, but that’s completely fixable.

Pro Tip: Not sure if Microsoft is blocking your emails because you can’t find any errors? You might have to go through some extra steps to find out if you’re receiving the 550 5.7.515 error. Learn how to find your Microsoft bounce codes.

What causes the 550 5.7.515 error?

For better or worse, the 550 5.7.515 error almost always comes down to something you did (or didn’t do). Which means you’re in control of fixing it. Here are the typical causes behind this error:

1. Your domain fails DMARC checks

DMARC (Domain-based Message Authentication, Reporting & Conformance) checks whether your email passes both SPF and/or DKIM and if those checks align with your “From” domain. If alignment fails, Microsoft might reject the message.

Think of it like airport security: even if your passport (SPF) and boarding pass (DKIM) are valid, if your name doesn’t match across both, you’re not getting on the plane.

2. SPF records are missing or incomplete

SPF (Sender Policy Framework) is a DNS record that lists the servers allowed to send mail on behalf of your domain. If your email comes from a server not listed there, Microsoft may consider it spoofed.

Plenty of senders forget to update SPF when adding new services (like CRMs, marketing platforms, or ticketing systems). One overlooked IP, and boom: 550 5.7.515.

3. DKIM isn’t set up or aligned

DKIM (DomainKeys Identified Mail) adds a digital signature to your email. Microsoft checks whether that signature can be validated and whether it aligns with your domain. If it doesn’t, that message gets denied.

4. You’re using a shared or poor-reputation IP

Even if your domain is clean, sending from a shared IP with a bad reputation can sometimes trigger this error. Microsoft’s filters consider sender reputation a big factor, and a poorly rated IP can tank your deliverability.

5. Policy enforcement from Microsoft

Microsoft has started aggressively enforcing domain alignment and authentication best practices. Their filtering systems are stricter than many other providers.

How to fix the 550 5.7.515 error

Check your DMARC, SPF, and DKIM records

Start with the basics. Make sure your DNS is properly configured:

• SPF: Lists all the IPs and services allowed to send on behalf of your domain.
• DKIM: Adds a digital signature that proves your message wasn’t tampered with.
• DMARC: Tells receiving servers how to handle messages that fail SPF or DKIM.

If any of these are missing, broken, or misaligned, Microsoft’s going to bounce your email.

Check your email authentication status for free with the domain checker:

Double-check SPF includes all sending services

If you’re using tools like Mailchimp, Salesforce, Zendesk, or anything else to send email, make sure their sending IPs are listed in your SPF record.

Each one needs to be explicitly authorized. Otherwise, Microsoft (and other mailbox providers) may flag those messages as suspicious.

And that’s a good thing, right? While you don’t want to see the 550 5.7.515 error message yourself, at least you know bad actors aren’t able to impersonate your brand.

Set up DKIM and match it to your domain

DKIM is required to pass DMARC, but passing isn’t enough. The domain used in the DKIM signature must align with your “From” address domain, or Microsoft may reject it.

Make sure your DKIM selector is publishing valid records, and that it’s tied to your root domain (or a properly aligned subdomain).

Align your DMARC policy and monitor results

DMARC alignment is often the deal-breaker. Your SPF or DKIM check might technically pass, but if they don’t align with your visible “From” domain, it still fails DMARC.

Use solutions like Valimail Monitor to review alignment and see which sources are passing or failing. Then adjust your records as needed.

Clean up your sending infrastructure

Old services, test accounts, and forgotten relays can all trip up authentication.

Audit who’s sending on behalf of your domain, remove anything unverified, and keep your records clean and current.

Improve your domain’s sending reputation

Sure, that’s easier said than done, but your sending reputation is everything. Even with perfect authentication, Microsoft may still block you if your domain or IP has a poor reputation.

Avoid spammy content, keep complaint rates low, and warm up new sending IPs slowly. Consistency builds trust over time.

How to prevent future authentication failures

Congratulations! You’ve fixed your 550 5.7.515 error. However, that doesn’t mean you should quit your email authentication progress. The next step is making sure it doesn’t come back. Microsoft (and other providers) are only going to get stricter about email authentication, so building a solid foundation now will save you major headaches down the road:

• Enforce DMARC alignment: Make sure your SPF or DKIM records align with the domain in your “From” address. Alignment is a must for DMARC to pass, and it’s often the hidden reason behind this error.
• Keep DNS records updated: Anytime you add a new sending service (like a marketing platform or helpdesk tool), update your SPF record and configure DKIM for that service. Don’t wait until emails start bouncing.
• Monitor with DMARC reports: Use DMARC reporting solutions to keep tabs on who’s sending email using your domain. This helps you catch misconfigurations or unauthorized senders before they cause problems.
  Use subdomains for third-party tools: Isolate external senders by giving them a subdomain (like info.yourdomain.com). It keeps your root domain protected and simplifies alignment.
• Gradually adopt a reject policy: Start with p=none, then move to quarantine, and eventually to reject. A stricter policy reduces spoofing and increases trust with mailbox providers.

The frustrating error with a silver lining

As annoying as the 550 5.7.515 error can be, it’s actually doing you a favor. It’s a sign that Microsoft is protecting its users and pushing senders to follow modern authentication standards. That’s a good thing for the entire email ecosystem (including your brand).

The fix isn’t complicated. It just requires visibility into your email authentication setup, and that’s exactly what Valimail Monitor is built for.

It’s free, fast to set up, and gives you complete insight into how your domain is being used. No more guessing. Just clarity, control, and a path to full DMARC compliance.

Stop errors before they happen.