550 5.7.511: banned sending IP: request removal by email

What it means

5.7.511 is an IP ban like the 5.7.606 to 5.7.649 range, with one difference: Microsoft wants to investigate traffic from the address before releasing it, so the self-service delist portal cannot be used. The bounce tells you to forward it to delist@microsoft.com. Microsoft asks for the full NDR code and the IP address, and says it will contact you within 48 hours with next steps. Use the time to find out why the IP was banned, since the investigation looks at the same traffic.

Common causes

• The IP sent spam, phishing or other traffic Microsoft judged harmful.
• A compromised server or account on your network used the IP.

How to fix it

1. 01Find and stop whatever sent unwanted traffic from the IP.
2. 02Forward the bounce to delist@microsoft.com with the full NDR code and the IP address.
3. 03Wait for Microsoft to contact you, which it says happens within 48 hours, and follow its instructions.
4. 04Do not use sender.office.com for this code; it does not handle 5.7.511.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

• External senders: use the delist portal to remove yourself from the blocked senders list and address 5.7.511 Access denied errorslearn.microsoft.com
• Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com

Further reading

• Blacklist checker
• The standard meaning of 550: mailbox unavailable