Has anyone dealt with Spamhaus blocking a server when the domain's configured IP address doesn't match the IP shown on the blocklist? For example, the domain resolves to 12.12.13.13, but Spamhaus reports 13.13.12.12. We're running on a VPS, and our provider initially said the listed address wasn't associated with us, although checking the address suggests that the VPS may be involved. What could cause this mismatch, and how can we identify and resolve it?
3 Answers
The IP your domain points to isn’t necessarily the only address involved. Check the server’s network configuration, outbound connections, NAT rules, and mail logs. A different interface or primary address may be sending the traffic, so capture traffic with tcpdump or tshark and verify the actual source IP.
Confirm exactly where the blocked IP appears. It might be the address used for outbound SMTP, a reverse-DNS/PTR record, or an address added by the hosting provider, rather than the address used by the website. Review DNS, PTR records, the VPS interfaces, and the provider’s network records together.
If this is related to email, inspect the mail logs first. A compromised mailbox, account, or mail server can send spam through the listed address. Find the account responsible, reset its credentials, secure the system, and follow Spamhaus’s delisting instructions only after the abuse has stopped.
The provider has since indicated that the listed address may be associated with the VPS, so checking for an abused account or compromised service is probably the next step.
Our provider initially said the listed address was unrelated, but their later information suggested it may actually be associated with the VPS. We’re checking the host configuration and traffic now.