What is an IP address and why it matters
An IP address is the unique numerical label assigned to a device or server when it connects to the internet. Think of it as your device’s postal address online: websites and services use it to send and receive data. There are two main types you’ll see: a private IP used on your local network and a public IP that the rest of the internet sees. If your public IP is flagged or blacklisted — often for sending spam, hosting malicious content, or getting compromised — you might notice email delivery problems, blocked connections, or poor reputation for services you run. Knowing how to find your IP and check its status can save you hours of headaches.
How to find your public IP address
Finding your public IP is usually straightforward. The quickest way is to open a web browser and search “what is my IP” or visit an IP display service. These pages instantly show the public IPv4 and IPv6 addresses your connection is currently using. If you prefer the command line, you can run a simple request: on macOS or Linux use curl against a public endpoint to return your address, and on Windows you can use PowerShell to do the same. Your public IP may change over time, especially if your ISP uses dynamic addressing, so make a note of it when you need to check listings or report issues.
How to find your local (private) IP address
Your device also has a private IP for your home or office network. On Windows, open Command Prompt and type ipconfig to see the IPv4 address for your network adapter. On macOS, open Terminal and use ifconfig, or get the active address with a dedicated command for the interface. On Linux, ip addr show lists network interfaces and their addresses. This private address is useful when troubleshooting routers or local services, but it is not used by the wider internet for blacklist checks.
How to check if your IP has been blacklisted
Once you have the public IP, the next step is to check whether it appears on popular blacklists. Many online tools and services will examine multiple blocklists and report any matches. Enter your public IP into a blacklist check tool and it will scan widely used DNS blackhole lists, spam databases and reputation services. If the IP appears on one or more lists, the tool usually displays which lists flagged it and links to details about the listing. For system administrators, command line DNS lookups against specific RBLs are also possible, but for most people the web tools provide an easy, readable summary.
What to do if your IP is listed
If you discover your IP is listed, the first step is not to panic. Confirm whether the listing is still active and gather details about which list flagged you and why. Some listings are temporary or due to misconfigured mail servers, compromised devices, or previous users of that IP behaving badly. If the listing is linked to spam or infected devices, stop the activity immediately: scan devices for malware, secure email servers with proper authentication and rate limiting, and close any open relays. For listings that relate to mail, ensure your server has correct reverse DNS (PTR) records, uses SPF, DKIM and DMARC, and follows good sending practices. Most blacklist providers offer a delisting or appeals process; follow their instructions and provide evidence that the issue has been resolved.
Preventing future blacklisting
Prevention is usually simpler than remediation. Keep all devices and servers patched and malware-free. Use strong passwords, two-factor authentication and firewalls. If you run mail services, authenticate correctly with SPF, DKIM and DMARC and avoid sudden spikes in outbound mail. If you’re on a shared hosting environment or a dynamically assigned IP from an ISP, be aware that other users’ behaviour can affect reputation. In such cases, consider asking your ISP for a static IP or a different allocation if problems persist. Monitoring your IP reputation regularly will help you catch issues early and stay ahead of problems.
When to contact your ISP or hosting provider
If the blacklist is due to activity you cannot control — for example because your ISP assigned you an IP that previously had a bad reputation, or because you suspect broader network abuse — contact your ISP or hosting provider. Explain the issue, provide the blacklist details, and request their assistance. Many providers have processes to investigate and, where appropriate, request delisting on behalf of customers. If your IP is dynamic and the easiest short-term fix is to obtain a new public IP, your ISP may be able to help with that too.
Monitoring and tools to keep an eye on reputation
Regular monitoring is the best insurance against surprises. Schedule periodic checks of your public IP and email server reputation, and subscribe to alerts where possible. Use reputable blacklist scanners and reputation services to track changes. If you run critical services, consider investing in a dedicated reputation monitoring solution that sends alerts when your IP or domain shows up on a list. Early detection makes remediation quicker and less damaging to your business.
Finding your IP address and checking whether it’s been blacklisted is straightforward and often reveals the root cause of email delivery failures and blocked connections. With a little routine monitoring, solid server configuration and good security practices, you can protect your IP reputation and avoid the hassle of delisting. If you need help diagnosing a listing, securing servers, or setting up ongoing monitoring, InfaCloud can help get you back to smooth, reliable online operations.
