550 5.7.511: Microsoft banned sender IP
550 5.7.511Access denied, banned senderPermanent: retrying will not helpFrom Microsoft 365 and Outlook.com
550 5.7.511 Access denied, banned sender [203.0.113.25]
What it means
A 5.7.511 rejection says Microsoft has banned the IP you are sending from. The wording usually reads like "Access denied, banned sender" followed by the IP and, often, removal instructions.
It looks like 5.7.606 but is handled differently. Microsoft’s own documentation does not send 5.7.511 through the self service delist portal; it asks for the removal request to include the full NDR and the IP, and the instructions printed in your bounce say where to send it. Treat 5.7.511 as the more serious of the two.
The owner of the sending IP must act. If that is a hosting provider or ESP, they are the ones who should file the request.
Likely causes
- The IP sent a large amount of spam or malware, often from a compromised server or web form.
- The IP belongs to a range with a long history of abuse that Microsoft blocked as a whole.
- An earlier 5.7.606 listing was removed and the IP went back to bad behaviour.
- You recently received the IP from a provider and the previous user ruined its reputation.
How to fix it
- Stop the source of bad mail first: audit the server for compromised accounts, open relays, and abused contact forms.
- Check the IP on public DNSBLs and clear those listings, since Microsoft looks for the same cleanup.
- Follow the removal instructions in the NDR exactly, quoting the full bounce and the IP; Microsoft 365 customers can also open a support case.
- While you wait, route mail for Microsoft recipients through a clean relay or a different IP with good reputation.
- Enroll the IP in SNDS and JMRP so you see future problems before they turn into bans.
Checks that apply
- Blacklist Check Shows which of 40 DNSBLs also list the IP, giving you evidence of abuse to clean up before asking Microsoft.
- Reverse DNS (PTR) A missing or generic PTR makes an IP look like a dynamic or compromised host; fix it before requesting removal.
- ASN Lookup Identifies the network owner, which tells you whether you or your provider should file the request.
FAQ
- Can sender.office.com remove a 5.7.511 ban?
- Usually not. The portal is built for 5.7.606 to 5.7.649 bans; follow the removal route given in the 5.7.511 NDR or ask Microsoft support.
- Will changing my HELO or From address get around it?
- No. The ban is attached to the IP, so only a removal or a different, clean IP changes the outcome.