Issue with Hotmail Delivery – 550 5.7.515 Authentication Rejection

Question

Issue with Hotmail Delivery – 550 5.7.515 Authentication Rejection

Latika Sharma 0

Dear Team,

We are facing delivery issues while sending emails from our domain to some Hotmail/Outlook recipients and also the emails are getting delivered on the same email addresses as well, so this issue is intermittent sometimes it's getting delivered and sometimes it's getting deferred soft.

Below is the bounce error received:

"550 5.7.515 Access denied, sending domain doesn't meet the required authentication level. The sender's domain in From address doesn't meet the authentication requirements defined for the sender."

Error Reference:

SPF = Pass
DKIM = Fail (as per bounce message)
DMARC = Pass

However, upon reviewing the original email headers from our side, we found that DKIM authentication is actually passing successfully.

We have verified the following:

SPF record is correctly configured and passing
DKIM is properly signed and showing pass in email headers
DMARC policy is configured and passing

Since the authentication appears valid from our side, kindly help us investigate why Microsoft's servers are still rejecting emails with authentication-related errors for some Hotmail recipients.

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Answer 1

Roebe Ta 1,545 Independent Advisor

Hello @Latika Sharma,

The "550 5.7.515" error indicates that Microsoft rejected your email because it didn't pass authentication checks. It's part of Microsoft's effort to enforce strong email authentication to reduce phishing and spam.

Microsoft has released an official article about this issue, you can learn more about it at Fix NDR error "550 5.7.515" in Outlook.com - Microsoft Support

If you've tried all the steps provided in the article but still couldn't resolved your issue, please kindly contact Microsoft Support Team for deeper analysis.

For business support:

Find your Microsoft 365 admin: If you don't know who the global admin is in your organization, you can find guidance here: How can I find my Microsoft 365 admin? - Microsoft Support
Submit a service request: The Global Administrator should create a support request with Microsoft to receive advanced technical assistance. For detailed instructions, see: Get support - Microsoft 365 admin | Microsoft Learn

If your subscription is from a partner or reseller, contact the reseller's support provider to help open a service request on behalf of you instead.

If you discover any solutions or have additional insights, please consider replying to this thread to help others in the community.

I sincerely apologize for redirecting you to the Microsoft Technical Support Team. While I strive to assist as much as possible here in the forum, my resources are limited when it comes to backend-level diagnostics and advanced troubleshooting. Some issues require deeper technical analysis and access to internal tools that only the official support team can provide.

If you need further assistance, feel free to reply. I'm here and happy to help!

Latika Sharma 0 Reputation points

2026-09-01T12:16:39.3266667+00:00

This is the issue where the same email address has got the email delivered and was bounced as well, so there are no authentication issues. If there was an authentication issue, then the email would have not delivered at all.
Roebe Ta 1,545 Reputation points Independent Advisor

2026-09-01T12:31:29.62+00:00

Thank you for the clarification. I understand your concern that some messages are successfully delivered to the same recipient while others receive a 550 5.7.515 rejection.

However, intermittent delivery does not necessarily rule out authentication-related issues. Authentication results can vary between messages depending on factors such as the sending infrastructure used, DKIM signing on individual messages, forwarding scenarios, or other signals evaluated during message processing.

As noted on the Outlook.com Postmaster site, Microsoft evaluates email authentication mechanisms including SPF, DKIM, and DMARC, and messages that do not meet the required authentication standards may be treated differently.

Because some messages are delivered successfully while others are rejected, the issue may require comparison of the successful and failed message traces to determine whether there are differences in authentication results or other factors that are only visible through internal diagnostic tools.

Besides opening a support request with Microsoft Technical Support, you can also contact Outlook.com Deliverability Support and providing examples of both successfully delivered and rejected messages, including the full message headers and timestamps. Microsoft's support team can compare the backend authentication evaluations and determine why certain messages are receiving a 550 5.7.515 rejection while others are accepted.

I hope this helps clarify why authentication can still be a contributing factor even when delivery is only intermittently affected.
Latika Sharma 0 Reputation points

2026-09-02T06:14:10.3733333+00:00

Just a question, how can I get the full message headers if the message is failed?
Roebe Ta 1,545 Reputation points Independent Advisor

2026-09-02T13:34:23.3833333+00:00

Hi @Latika Sharma,

For messages that fail with a 550 5.7.515 rejection, you generally cannot obtain the full message headers from the recipient side because the message was never delivered to the mailbox.

If available, you can share the full message headers from a message that was successfully delivered to the same Hotmail/Outlook recipient, along with the complete NDR/bounce message and timestamp for a failed delivery attempt instead.

I hope this helps point you in the right direction.