Outlook.com / MSN Account Rejecting Valid Mail with 5.7.1

The abbreviated 5.7.1 line does not establish a restriction on your MSN mailbox; obtain the complete non-delivery report (NDR), then route it either to the sender’s mail administrator or to Outlook.com in-product support based on its detailed diagnostic code.

1. Obtain the complete NDR

Ask an affected sender to provide the entire bounce message, especially:

• The full SMTP response beginning with 550 5.7...
• Diagnostic information for administrators
• The sending server’s IP address
• Any identifiers such as S3150, 5.7.515, “blocked,” “authentication,” or “delivery not authorized”
• The timestamp and Outlook protection-server name

They should redact personal addresses but retain server names, IPs, codes, and message IDs. 5.7.1 is a family of permanent policy/security failures—including authorization, relay, and authentication failures—so the text following the code determines the responsible side.^1^

2. Route the issue according to that diagnostic text

If the NDR names the sender’s IP, blocklist, reputation, SPF, DKIM, DMARC, reverse DNS, or authentication:

The sender or their email provider must handle it. Safe Senders cannot override a rejection that occurs while the sending server is handing the message to Outlook.com.

Ask the sender’s mail administrator or ISP to:

1. Check the reputation of the exact outbound IP shown in the NDR.
2. Validate reverse DNS and the domain’s SPF/DKIM/DMARC configuration.
3. Follow Outlook.com Sender Support.
4. If their configuration complies with Microsoft’s requirements but delivery still fails, submit the deliverability issue through the sender-support troubleshooting form.

That form specifically covers delivery to @msn.com, @outlook.com, @hotmail.com, and @live.com addresses.^2^

If the full NDR identifies your MSN address as disabled, nonexistent, restricted, or rejected independently of the sender—and unrelated senders using different providers receive the same diagnostic:

Escalate through authenticated Outlook.com support:

1. Sign in to Outlook.com in a browser.
2. Select Help from the top menu, then Help.
3. Enter a concise description such as:
   Multiple unrelated providers receive the same 550 5.7.x rejection when sending to my MSN address. Mailbox storage, rules, forwarding, blocked senders, and Safe Senders have already been checked.
4. If self-help does not resolve it, scroll to Still need help? and select Yes.
5. Include sanitized copies of the complete NDRs, timestamps, sender domains/providers, sending IPs, and the fact that the messages never reach Junk.

This is the documented route for Outlook.com email support and is the appropriate channel for requesting backend investigation.^3^

Microsoft Learn Q&A cannot access consumer mailboxes, inspect server-side restrictions, or directly escalate a mailbox to the Outlook.com engineering team.

Important distinction

The rejecting hostname and IP show that Outlook.com’s protection service issued the rejection, but they do not by themselves show that your mailbox is restricted. Outlook.com may reject a message because of the sending IP or domain even while your mailbox continues receiving messages from other providers. Microsoft’s receiving-mail guidance directs senders of specific missing messages to Outlook.com Sender Support.^4^

Since you have already checked storage, rules, forwarding, blocked senders, Safe Senders, sign-in state, and Outlook.com itself, those mailbox-setting steps do not need to be repeated. The next discriminating evidence is the complete NDR from at least two affected senders, preferably using different email providers.

References

1. Email nondelivery reports and SMTP errors in Exchange Online
2. Sender Support in Outlook.com | Microsoft Support
3. How to get support for Outlook.com
4. Can't send or receive email in Outlook.com | Microsoft Support