Anti-Spam DNSBL  
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Use of the nsZones DNSBLs is free of charge for everybody. You can use nsZones public mirrors free by setting your mail server's DNSBL feature to query bl.nszones.com

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Professional DNSBL

Synchonize option is available for internet ISPs, organizations, networks, hosting providers, email providers.

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The sbl.nszones.com Block List
The sbl.nsZones.com is a realtime database of open-relay hosts, spammers hosts, open proxies, spam engines.

All hosts in this list are periodically (every 12 months) re-checked and the secured hosts are automatically removed from our databases.

SBL contains IPs received from:

SPAM Sources
The addresses are gotten from E-Mail that we have received that was SPAM.

Bulk mailers
that don't require confirmed opt-in from their customers, or that have allowed known spammers to become clients and abuse their services.

Open Relays, hijacked PCs
IPs exhibiting characteristics which are specific to open proxies and dedicated Spam BOTs which have been abused to send spam, worms/viruses that do their own direct mail transmission.

If you have inherited such IP address space, please let us know and we will remove you, but should we get additional SPAM from your IP will be added back to the list.

Note: SBL does not block SPAM comming from dynamic or no PTR networks.

Spam List Usage

DNSBL queries are structured by the inverse IP address as a subdomain of the DNSBL zone. For example, to check that the general DNSBL test address of is listed in SBL, query with any NS lookup tool such as...

You will receive an address: - Open Relay, Hijacked PCs, Spam Source

sbl.nszones.com is included in bl.nszones.com

Attention: SBL is checking only IPs and not Domain Names.
Do not use sbl.nszones.com to check Domain Names.
For Domain Names check please use ubl.nszones.com

How to use nsZones Services
Doing a DNSBL lookup on a message at SMTP connect time is cheap in hardware cycles and system time. Your DNS server may even have it cached from the last time the spammer tried.

Mail rejected by a DNSBL during delivery is not silently discarded or lost. A DNSBL realtime rejection creates a delivery status notification to the sender identifying the cause of the rejection, thereby allowing troubleshooting on the sender's end.

By rejecting the connection attempt in real-time, a DNSBL also avoids any problems associated with an email system accepting delivery, closing the connection, and then trying to return the mail to a potentially forged address after the message is determined to be spam.

DNS is inherently very efficient, using minimal amounts of bandwidth. Using BL will use much less bandwidth than having to accept every spam and virus email sent to your email system. By rejecting these spam messages during the SMTP connection, no further data is sent thereby reducing overall bandwidth requirements. DNS caching by your local DNS server also prevents redundant queries from utilizing excessive bandwidth.

The use of the nsZones DNSBLs is free of charge for low-volume non-commercial use.

For professional use, internet ISPs, or hosting providers, we can provide your unlimited or dedicated realtime access to all nsZones DNSBLs from your network.

Free mirror service is provided to sites who are willing to host a public mirror (serving data to other free users).

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