IP blacklist checker
If your mail is disappearing, the first thing to rule out is that your sending address is on a blocklist. These are the lists receiving servers actually query, checked the same way they check them.
Free, no signup, no daily limit. We do not store what you check here.
What a listing actually means
A blocklist entry is not a verdict on you, it is a record that something unwanted came from that address recently. On shared hosting or a cloud provider that may have been another tenant entirely. It still affects your delivery, because receiving servers look at the address rather than at who was using it.
Getting delisted
Each list runs its own removal process, and most publish a self-service form. Delisting without fixing the cause guarantees a relisting within days, so the order is: find what sent the mail, stop it, then request removal. Spamhaus is the one worth prioritising - a listing there affects delivery almost everywhere, while some of the smaller lists are consulted by very few servers.
Questions
I am not listed but my mail still goes to spam. Why?
Blocklists are only one input. Authentication, sending reputation, content and complaint rates all matter, and a new sending domain has no reputation at all whatever its DNS says.
Should I check my domain or my IP?
This checks the IP that sends your mail, which for most people is their provider rather than themselves. If you send through Google, Microsoft or a transactional service, their address is what gets checked - and their reputation is what you are relying on.
Related tools
IP address checker
Check whether an IP address is public, private, reserved or carrier-grade NAT. Free, no signup, IPv4 and IPv6.
Datacenter IP checker
Check whether an IP belongs to a hosting provider such as AWS, Google Cloud or Hetzner rather than a home connection. Free.
Email deliverability check
One check for MX, SPF, DMARC and DKIM on your sending domain, with what to fix first. Free, no signup.
When you need more than a free tool
This page answers what can be determined offline and from public DNS. The API adds live carrier and mailbox verification, a calibrated confidence score, and the full evidence trail behind every verdict.
Credits never expire. Inconclusive verdicts are never billed. Cancel in one call. See pricing or read the docs.