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SenderProbe
Reputation check

Check an address against the blocklists receivers query

Reputation is judged before a filter reads a word of your message. SenderProbe resolves the addresses behind a domain, queries every blacklist zone it knows in parallel, and returns the listing reason and the delisting route for each one that answers.

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How a receiver queries a blacklist

A DNSBL is a DNS zone rather than a downloadable list. To ask whether an address is listed, a mail server reverses the octets, appends the zone name and makes an ordinary A query. An answer inside 127.0.0.0/8 means listed, and the last octet usually says which sub-list matched; NXDOMAIN means not listed. Many zones publish a TXT record alongside the answer explaining why.

The whole exchange costs one cached DNS query, which is why an email blacklist check happens during the SMTP conversation and why a listing rejects mail rather than filing it.

The same query against one zone for two addresses in 203.0.113.0/24: the first is listed, and the empty answer for the second means it is not.
$ dig +short 10.113.0.203.dnsbl.example.net
127.0.0.4

$ dig +short 11.113.0.203.dnsbl.example.net
$

Which listings actually cost you delivery

They are not equal. A listing on a zone the large mailbox providers consult directly stops mail outright. A listing on a zone that escalates to whole network ranges, or that lists an address because a neighbour on the same /24 misbehaved, is worth knowing about and rarely worth panicking over — some of those zones exist mainly to sell removal.

SenderProbe grades each zone by how much receivers really weigh it, and notes the zones whose listings are an artefact of the range rather than of anything you sent. A single low-impact listing beside a clean result everywhere else is usually not the reason your mail is being filtered.

Getting delisted

Fix the cause first: a compromised account relaying through your server, an open relay, a list you mailed without consent, or a forwarding setup returning other people's spam. A delisting request against an address that is still sending will be reversed within the day, and repeat requests are noticed.

Then use the zone's own form. Most operators publish one, several delist automatically once the traffic stops, and a few charge — which tells you how much weight to give them. SenderProbe returns the delisting URL for every zone that lists the address, so the route is in front of you rather than behind a search.

The IP blacklist is only half the question

Domain and URI blocklists list names rather than addresses, and they are checked against the domains that appear in a message: the sending domain, the links in the body, the domain in the reply-to. Moving to a new sending address does nothing about a listing of that kind.

A blocklist entry on a shortened link or a tracking domain you did not know was in the template is a common cause of filtering that looks inexplicable from the sending address alone, which is why the check covers both the addresses behind a domain and the domain itself.

What the blacklist check reports

  • Every zone queried, with the addresses behind the domain that were tested.
  • The return codes and the reason text a listing zone published.
  • How much weight receivers give each zone that returned a listing.
  • The delisting URL and any caveat worth reading before you use it.
  • Zones that failed to answer, kept separate from zones that answered not listed.

Run this check on your own domain. A workspace takes a minute to create and runs every one of the eleven checks against the domain you name.

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Common questions

How do I know if my IP is blacklisted?
Query the address against the DNSBL zones receivers actually use, rather than checking one list at a time. A blacklist check resolves the addresses behind your domain and asks every zone in parallel, returning the listing reason where the zone publishes one. Bounce messages are the other signal: many receivers name the blocklist in the rejection text.
How long does delisting take?
It depends on the zone. Several delist automatically once the address stops sending abusive traffic, typically within a day or two. Others process a manual request in hours. None of it lasts if the cause is still running, so find the compromised account, the open relay or the unconsented list before submitting the request.
Does one blacklist listing stop my email?
Not necessarily. Receivers weigh the zones differently: a listing on one that the large mailbox providers consult will reject mail outright, while a listing on a low-impact zone may cost you nothing measurable. What matters is which zone, and whether the listing describes your address specifically or the whole range it sits in.
What is the difference between an IP blacklist and a domain blocklist?
An IP blacklist lists sending addresses and is queried when a mail server connects. A domain or URI blocklist lists names, and is queried against the domains in the message itself, including the links in the body. Changing your sending address clears the first kind and has no effect at all on the second.
Why is a brand-new IP address already listed?
Because the listing is about the range or the previous tenant, not about you. Address space that has been used for bulk mail carries its history, and some zones list entire blocks a provider has designated as dynamic or residential. Check the listing reason: if it describes the range, the fix is with the provider rather than with you.

Keep reading

Related checks, definitions and guides.