Ask DNS. Get a verdict before you deliver.
A DNS blocklist for connecting IP addresses, split by how new and how persistent the abuse is.
Query it with a plain A lookup from any mail server or resolver. No account, no key.
01The zones
fresh
New in the last 24 hours. Catches a sender as it starts.
spam
New in the last 7 days. The general-purpose list.
repeat
Seen more than once in the last 28 days. Persistent offenders.
ms
Microsoft cross-tenant ID rather than an IP. Listed for 7 days.
02The domains
Every domain carries the same four zones with the same data, so you can use whichever suits you or query several for resilience.
| Domain | fresh | spam | repeat | ms |
|---|---|---|---|---|
| dnsbl.uk | fresh.dnsbl.uk | spam.dnsbl.uk | repeat.dnsbl.uk | ms.dnsbl.uk |
| dnsrbl.us | fresh.dnsrbl.us | spam.dnsrbl.us | repeat.dnsrbl.us | ms.dnsrbl.us |
| dnsbl.eu | fresh.dnsbl.eu | spam.dnsbl.eu | repeat.dnsbl.eu | ms.dnsbl.eu |
| dnsbl.au | fresh.dnsbl.au | spam.dnsbl.au | repeat.dnsbl.au | ms.dnsbl.au |
03Query it
dig a 4.3.2.1.repeat.dnsbl.eu
dig txt 4.3.2.1.repeat.dnsbl.eu| Answer | Meaning | Typical action |
|---|---|---|
127.0.0.2 | Listed in this zone | Reject or score, per zone |
NXDOMAIN | Not listed in this zone | Accept |
A TXT query on a listed entry returns a short human-readable reason. Draft return codes: final values still to be decided.
Using this in production?
Read the policy and usage limits first, and always fail open: a DNSBL answer should be one signal, not the only one.