Microsoft sending-IP reputation block

Outlook 550 5.7.511: Access denied, banned sender

Microsoft uses 5.7.511 when the sending IP is banned. Stop the source of abusive traffic, secure the system, and then use Microsoft's current delisting route with the full NDR and IP.

Problem description

The NDR reports:

550 5.7.511 Access denied, banned sender

Available automated evidence: MailFixIt can check the supplied IP against SpamCop and verify PTR, forward DNS, and its network owner. It cannot inspect or remove Microsoft's private reputation block, and it does not offer a reputation repair.

Run automated checks on this sending IP

Enter your sending domain and public sending IP. MailFixIt checks SpamCop, PTR, forward-confirmed reverse DNS, and the network owner. These public signals cannot reproduce a mailbox provider's private reputation decision. MailFixIt does not offer a Fix Pack for IP reputation; a confirmed PTR problem is handled separately.

Is this temporary or permanent?

The 550 response is permanent for each blocked attempt. Do not continue unchanged traffic.

Before delisting

Stop compromised users, forms, APIs, and open relays.
Inspect outbound queues and unusual recipients.
Rotate credentials and revoke malicious tokens.
Confirm list consent, bounce suppression, and complaint handling.
Identify shared-IP responsibility with the provider.

Recovery sequence

Record the full NDR and exact sending IP privately.
Remove the root cause and drain malicious queues.
Verify legitimate traffic meets Microsoft sender practices.
Use Microsoft's current delist portal or documented support route.
Resume gradually and monitor for recurrence.

Frequently asked questions

What does Microsoft 5.7.511 mean?

Microsoft banned the IP address used to send the message.

Should I request delisting immediately?

First stop the abusive or compromised traffic. Delisting without remediation can lead to another block.

Can changing SPF remove the IP ban?

No. Microsoft controls the block and its delisting process.

Related email diagnostics

Outlook 451 4.7.500-699: Access denied, please try again laterResolve Microsoft 451 4.7.500-699 by keeping slow retries and investigating the changed IP volume or suspicious sending activity. Gmail 550 5.7.28: There is an unusual rate of unsolicited email originating from your IP addressResolve Gmail 550 5.7.28 when unusual unsolicited email from a sending IP is permanently blocked for the attempt. Yahoo 554 Message not allowedResolve Yahoo 554 Message not allowed by using the full response to distinguish authentication, content, reputation, and sender-policy causes.

Primary sources: Microsoft Exchange Online NDR reference.