Check an IP or domain against mail blocklists
When your mail vanishes without any error message, the sending server’s IP address is often on a blocklist. Which list matters enormously — and so does knowing which lists nobody can check from outside.
- Runs from your browser, not our server
- No sign-up
- No watermark
Loading the tool…
How it works
- Enter the IP address of the server that sends your mail (or a domain to check the domain lists).
- Read the table: each row says what that list reports, and links to its own removal page.
- For an IP, check the reverse DNS block too: it shows the name registered for that address. A missing or non-matching name hurts delivery on its own.
Why nothing is uploaded
Every operation on this page is done by code running inside your browser tab, using the same engine that renders web pages. The file is read from disk into your tab’s memory, transformed there, and written back out as a download. It is never sent anywhere — not to us, not to a third party.
Verify it yourself
- Open your browser’s developer tools (F12) and select the Network tab.
- Load your file and run the tool.
- The only requests you will see fetch the tool’s own code — and, for a few heavy tools, their open-source engine from a public CDN — plus one small page-view ping to loreatec.jp (page address and title, nothing more). None of them carry your file.
Frequently asked questions
Why are Spamhaus and URIBL not checked?
They deliberately refuse questions arriving through public DNS services like Cloudflare and Google, which is the only route a browser has. Spamhaus answers with a code that means “open resolver — I will not tell you”, URIBL with a refusal. Treating that as “not listed” would be exactly the wrong conclusion, so they are listed separately with links to their own lookup pages, which are free for occasional use.
I am on one list out of fifteen. How bad is that?
It depends entirely on the list. Some are consulted by a large share of the world’s mail servers; others by a handful. Read what the row says, follow that list’s own removal process, and fix whatever put you there — a hacked account, a wrongly configured mail server, or a shared IP where someone else did the damage. Nobody else can remove you, and no service that offers to “delist you from 100 blocklists” can either.
What is forward-confirmed reverse DNS?
Every IP address can have a name registered for it (the reverse name). Forward-confirmed means that name also points back to the same IP. Many receivers check this, and a mail server whose reverse name is missing or does not match is treated as suspicious before the message is even read. Your hosting provider sets the reverse name; you set the forward one.
Why does one row say “whitelisted”?
One of the lists — HostKarma — uses the same lookup for both its allow-list and its block-list, told apart by the answer code. Being on its allow-list is good news, so it is shown as that rather than as a listing.
Does the blocklist see my IP address?
No. The question goes from your browser to the public DNS service, and that service asks the list. The list sees Cloudflare’s or Google’s address, not yours.