Issue with Hotmail Delivery – 550 5.7.515 Authentication Rejection

Question

Issue with Hotmail Delivery – 550 5.7.515 Authentication Rejection

Moiz Shaikh 0

Dear Team,

We are facing delivery issues while sending emails from our domain [Moderator note: personal info removed] .COM to some Hotmail/Outlook recipients.

Below is the bounce error received:

"550 5.7.515 Access denied, sending domain [Moderator note: personal info removed] .COM doesn't meet the required authentication level. The sender's domain in the [Moderator note: personal info removed] .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

Please note that our forum is a public platform, and we will modify your question to hide and move your personal information in the description to a private message to avoid exposing any personal or organizational information. Please refer to the private message for those details. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Hi Moiz Shaikh

The error message 550 5.7.515 Access denied occurs when Microsoft blocks emails from a domain because authentication checks (SPF, DKIM, or DMARC) are not validated correctly.

Since you have confirmed that DKIM did not validate successfully (specifically on Microsoft’s servers), this strongly suggests that Microsoft’s protection systems are identifying a DKIM validation issue for the affected domain, rather than applying a general block based on the TLD.

In Microsoft 365 / Outlook.com, even if SPF and DMARC validate correctly, a DKIM validation issue alone can still trigger delivery restrictions, especially when the domain’s reputation is still being evaluated or when the domain is considered higher risk.

Please note that as forum moderators, we do not have direct access to Microsoft’s sender reputation systems, block lists, or mail transport filtering policies. For reputation review requests and IP/domain mitigation, please contact Support directly. For more details, please visit the Announcements section.

Reference:

Fix NDR error "550 5.7.515" in Outlook.com - Microsoft Support

Thank you for your patience and understanding.

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Moiz Shaikh 0 Reputation points

2026-05-06T05:57:16.58+00:00

Hi,

As I tested by sending emails to other Hotmail accounts (including my own test ID), the emails were delivered successfully and all authentication checks are passing correctly.

However, when sending emails specifically to the affected recipient, the emails are failing with an authentication-related error.
Hani-Ng 10,575 Reputation points Microsoft External Staff Moderator

2026-05-06T06:33:32.07+00:00

Hi Moiz Shaikh

Successful delivery to other Hotmail/Outlook.com accounts, alongside passing SPF, DKIM, DMARC, and CompAuth results in the headers, suggests that the sending configuration is generally being accepted by Outlook.com. When delivery issues occur only for a specific recipient, error 550 5.7.515 may be related to recipient‑specific trust or reputation evaluation, rather than a domain‑wide authentication failure.

Outlook.com applies composite authentication and filtering decisions that can vary per recipient and over time, even when authentication checks appear to pass. In such cases, forum moderators do not have visibility into or control over the recipient‑level enforcement that may be applied.

For scenarios like this, I recommend submitting the sending domain and IP for review via the sender support channel so the deliverability team can evaluate the situation further: https://sender.office.com

I hope this information helps.

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Issue with Hotmail Delivery – 550 5.7.515 Authentication Rejection

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