At a glance. Lookup: DNS, over the list's domain · Result: Listed, clean or unknown · First step: Find the cause, then request removal · Tool: Blocklist check
The short version
- Why check. Mail is refused or filtered when a receiving server finds the sender on a list it trusts.
- Find what to check. Blocklists list IP addresses and domains.
- Run the check. Enter the IP or domain in our blocklist check.
- Read the result. Each list has its own meaning.
- Find and fix the cause. Do not ask for removal first.
- Request removal. Open the list's own lookup page, which shows the reason for the listing and how to be removed.
Why check
Mail is refused or filtered when a receiving server finds the sender on a list it trusts. If your messages suddenly bounce with a policy message, or deliveries to many providers drop at once, a listing is one of the first things to rule out.
Check before you start sending from a new IP, regularly while you send, and whenever bounces mention a list or a block.
Find what to check
Blocklists list IP addresses and domains. The IP that matters is the one your mail leaves from, which you can read from the Received lines in the headers of a message you sent. The domain that matters is the one in your From address and your links.
If you send through a provider, you share IPs with other senders unless you have a dedicated IP. A listing on a shared IP is the provider's to fix, and it is worth telling them.
Run the check
Enter the IP or domain in our blocklist check. It queries each list over DNS and shows, for each one, whether the address is listed, clean or unknown. A DNS blocklist works by looking up a name made from the address, which is how mail servers check a sender in milliseconds.
For an IP address the name is made by reversing the numbers and adding the list's domain. If the name does not exist, you are not listed. If it returns an address starting with 127, you are listed and the exact value says why.
Read the result
Each list has its own meaning. A listing on a list of exploited machines points to malware or a compromised account, a listing on a spam-source list points to what you sent, and a listing on a list of ranges that should not send mail directly points to your IP type, such as a home or dynamic address.
If a list returns unknown, it may have refused the query because it came through a large shared resolver. Check it on its own website using the link in the result.
Find and fix the cause
Do not ask for removal first. A listing is a symptom, and removal without a fix leads to a relisting. Look for a compromised mailbox or website form that was used to send spam, a list with addresses that never agreed to hear from you, a sudden jump in volume, and missing authentication.
Stop or reduce sending from the listed IP while you work. Then fix the cause, and document what you changed, because some lists ask for it.
Request removal
Open the list's own lookup page, which shows the reason for the listing and how to be removed. Some lists remove an entry automatically after a period with no further reports, some need a request, and a few ask for payment, which is a reason to take care before you pay anyone.
Removal can take hours or days. Check again afterwards, and watch your bounces and complaint rates, which tell you more about real delivery than the list status does.
Stay off blocklists
Send only to people who asked to hear from you, confirm sign-ups, validate addresses, and remove bounces and complaints at once. Authenticate your domain with SPF, DKIM and DMARC, and ramp up volume gradually on a new IP.
Secure your sending accounts and API keys, because compromised credentials are a common cause of listings. Monitor your IP and domain regularly so you find a problem early.
Further reading and sources
Do it in MigoSMTP: help-center articles
- Check and remove a blocklist listing
- Emails going to spam: troubleshooting checklist
- Gmail, Yahoo and Outlook bulk sender checklist
Related guides and tools
- Blocklist check: Look up an IP or domain now.
- IP warm-up calculator: Plan a safe ramp.
- SPF, DKIM and DMARC checker: Authenticate your domain.
- Email bounce types: Read a block bounce.
Want help planning your volume? Tell us what you send and we will suggest a setup.
Frequently asked questions
How do I check if my IP is blacklisted?
Enter the sending IP address in a blocklist checker, which queries each list over DNS and reports whether the address is listed. Also read your bounce messages, which often name the list that refused the message.
Does being on a blocklist mean my mail is blocked everywhere?
No. A listing only affects receivers that use that particular list, and how they react varies. Large providers rely mostly on their own reputation systems, so check your bounces and complaint rates for the real effect.
How do I get delisted?
Find out why you were listed, fix the cause, then follow that list's own removal process. Some listings expire on their own. Asking for removal without fixing the cause usually ends in being listed again.
Why does the checker say a list is unknown?
Some lists refuse queries that arrive through large shared DNS resolvers, or the lookup timed out. Unknown is not the same as clean, so check that list on its own website.