5.7.511: Access denied, banned sender (IP)
Microsoft returns 5.7.511 when the IP you are sending from has been banned. Unlike the 5.7.606 range, Microsoft’s documented fix is to email delist@microsoft.com with the full NDR code and the IP address, after making sure whatever caused the ban has stopped.
The exact message
Microsoft 365 / Exchange Online
5.7.511 Access denied, banned sender
Why it happens
- Spam or abusive traffic from the sending IP.
- A recycled IP that inherited a previous owner’s ban.
How to fix it
- Stop and investigate any bulk or unexpected traffic from that IP.
- Email delist@microsoft.com with the full NDR code and the IP address.
If you send cold email
Moving to a different IP without fixing the sending pattern usually gets the new IP banned too.
How WarmHawk handles it
WarmHawk pauses a mailbox on its own once its hard-bounce rate passes 5% over at least 20 sends, and pauses a campaign at that campaign’s own bounce threshold, so a bad list stops before it drags the domain down. Every sending domain is re-checked against DNS blocklists hourly, and a mailbox only reaches campaign volume after at least 14 days of warmup with a 90% inbox rate. A mailbox whose inbox rate falls below 70% goes back to warmup. How WarmHawk works →
Check your domain now
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Related bounce codes
Sources, checked 2026-09-29: Microsoft Learn: NDRs and SMTP errors in Exchange Online · Microsoft Learn: Use the delist portal. Have a different bounce? Paste it into the decoder →
Questions
5.7.511 questions
What does 5.7.511 mean?+
Microsoft returns 5.7.511 when the IP you are sending from has been banned. Unlike the 5.7.606 range, Microsoft’s documented fix is to email delist@microsoft.com with the full NDR code and the IP address, after making sure whatever caused the ban has stopped.
Is 5.7.511 a temporary or permanent error?+
Permanent. The message will not be retried, and sending it again unchanged will fail the same way until the cause is fixed.
How do I fix 5.7.511?+
Stop and investigate any bulk or unexpected traffic from that IP. Email delist@microsoft.com with the full NDR code and the IP address.