The nsZones SURBL/Spam URI Realtime Block List (UBL) is a domain-based blacklist that helps filter spam by identifying website domains found in unsolicited emails, differing from a typical IP-based blocklist which checks server addresses instead.
The nsZones SURBL/Spam URI Realtime Block List (UBL) is a type of blacklist, specifically a SURBL (Spam URI Realtime Block List). SURBLs are curated lists of domain names that have been observed within the content of unsolicited or spam emails.
Unlike a traditional IP-based blocklist, this list focuses on Uniform Resource Identifiers (URIs), which are essentially the domain names found in an email's body. For example, if the domain 'spamwebsite.com' is included in a marketing email, and that domain is on the ubl.nszones.com blacklist, receiving mail servers that use this list may filter the message as spam.
Technically, mail servers use the DNS system to check if a domain is listed. A DNS query for 'spamwebsite.com.ubl.nszones.com' will return a specific IP address, such as 127.0.0.4, if the domain is on the blocklist. This response signals to the mail server that a blacklisted domain was found.
The nsZones SURBL/Spam URI Realtime Block List (UBL) is operated by nsZones. The organization runs a system that identifies spam sources using DNS-based lists (also known as DNSBLs or RBLs). This allows email server administrators to check if an incoming email connection or a domain within a message is associated with known spam activity.
nsZones operates with the philosophy that its lists are defensive tools intended to help email receivers filter unwanted mail at their discretion. The organization maintains several different types of lists, including IP-based blacklists and domain-based blocklists (SURBLs).
In addition to its domain-based UBL, nsZones runs the following lists:
The service is supported in part by a network of public mirrors, which allows volunteers to host copies of the nsZones blacklists to help distribute the DNS query load.
Before requesting removal from any blocklist (or blacklist), you must first identify and resolve the underlying issue that led to the listing. This might involve cleaning a hacked website, securing a compromised email account, or fixing a misconfiguration. If the core problem is not addressed, your domain will likely be listed again.
nsZones provides two options for delisting from the nsZones SURBL/Spam URI Realtime Block List (UBL):
To check your domain's status and request removal, you can use the official nsZones delisting form.
The overall impact of a listing on the nsZones SURBL/Spam URI Realtime Block List (UBL) is considered low. It is not widely adopted by major mailbox providers like Gmail, Microsoft Outlook, or Yahoo.
Despite its low impact score, a listing can still cause deliverability issues. Some corporate mail servers, smaller internet service providers, and spam filtering appliances may use this blocklist. Since it is a SURBL (a domain-based blacklist), the negative effect is tied to the content of your emails. Any message containing a link to a listed domain may be blocked or filtered to the spam folder, even if the sending IP address has a good reputation.
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