The ZapBL DNSBL is an IP-based blocklist (blacklist) where listings are created by ZapBL administrators based on spam received directly to their private email addresses and spam traps.
ZapBL DNSBL is a DNS-based blocklist (DNSBL) that lists IP addresses its administrators no longer wish to receive email from. According to its operators, it is a list of opinions, not a definitive declaration of a sender being a spammer. Any mail server administrator can query this blacklist to help filter incoming email, but usage is at their own discretion. The ZapBL project encourages those who use the list to inform them.
The listing policy is based on spam messages received at email addresses controlled by ZapBL administrators. These addresses can include personal accounts, dedicated spam traps, or catchall addresses. Listings are created manually by an admin or through an automated process that includes a manual review. Critically, ZapBL does not accept third-party reports or submissions for its blocklist.
Technically, ZapBL is an IPv4-based blocklist. Mail servers query it using the zone dnsbl.zapbl.net. A query is performed by reversing the octets of an IP address and prepending it to the zone name. For example, the IP 192.168.1.2 would be queried as 2.1.168.192.dnsbl.zapbl.net. A positive result will return the code 127.0.0.2, which indicates a listing.
The ZapBL DNSBL is maintained by a group known as the ZapBL admins. The project is based entirely on the mail they receive and their personal judgment of what constitutes unwanted email. To protect the integrity of the system and prevent targeted attacks, the administrators' email addresses and identities are kept confidential and are not disclosed.
Before requesting removal from this blocklist, you must first identify and fix the root cause of the listing. This could involve securing a compromised server, removing a user account sending spam, or reconfiguring your mail server to stop sending backscatter. Once you have resolved the issue, you can pursue one of the following delisting paths.
ZapBL states that they will only communicate with the registered abuse contact for an IP block. End-users who find their IP on the blacklist should contact their Internet Service Provider for assistance. There is also a paid option for express delisting with a manual review, which can also be requested through the contact form.
The impact of being listed on the ZapBL DNSBL is generally considered to be low. It is not one of the major blocklists used by large mailbox providers like Google or Microsoft. Its primary users are more likely to be smaller organizations or independent mail server administrators who have chosen to incorporate this specific list into their anti-spam policies.
However, even a listing on a low-impact blacklist can cause email delivery failures. If you send email to a recipient whose mail server uses ZapBL, your messages will likely be rejected or sent to the spam folder. Therefore, it is always best to investigate and request removal to ensure maximum deliverability.
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