Inclusion in the Spamhaus-ZEN Blacklist results from sub-listings in one or more the following Blacklists:
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CBL - You have contracted a virus or malware that is operating a botnet, either on your email server on a workstation behind the NAT - Continual delisting requests without eliminating the virus will result in permanent blacklisting
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XBL - (Spamhaus Exploits Block List) is a real-time database of IP addresses of hijacked PCs infected by illegal 3rd-party exploits, including open proxies
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PBL - Spamhaus PBL is a DNSBL database of end-user IP address ranges that should not be delivering unauthenticated SMTP email to any Internet mail server except those provided for specifically by an ISP for that customer's use
Spamhaus Zen Reports Dynamic Ip Addresses
Dynamic-based Blacklists will list many DHCP ranges of IP Addresses from Internet Service Providers. You could be listed if your IP Address was previously dynamically assigned, or if your ISP gave you a static assignment and did not assign a distinguished PTR-Record, aka a "Reverse DNS Entry."
Spamhaus Zen Reports Open Relays
Relay/Proxy-based Blacklists typically list email servers and/or hostnames that are sending Unsolicited Bulk Email (UBE) that is clearly from email addresses that are not hosted on the server or that do not match the SMTP Banner/Hostname of the Email Server, commonly referred to as an Open Relay. An Open (Mail) Relay is an SMTP server configured in such a way that it allows anyone on the Internet to send e-mail through it, not just mail destined to or originating from known users.
Spamhaus Zen Reports Sources Of Spam
Spam-based Blacklists are those that will list either single IP Addresses or entire ranges that have actually received Spam, i.e. Unsolicited Bulk Email (UBE) in their Spamtraps from an IP-Address. This could be a result of a compromised email account, an Open Relay, or simply sending mass emails / marketing and not following best practices according to the "CAN-SPAM Act of 2003" (ref: https://en.wikipedia.org/wiki/CAN-SPAM_Act_of_2003)
Spamhaus Zen Reports Virus Infected Sources
Virus-based Blacklists are those that will list single IP Addresses (or hostnames) of email servers that have sent Spam traffic that is generated by some form of a Virus, Malware, Trojan, or "botnet" infection in a network. This is often a result of a user visiting a webpage that houses an infection and downloads malware on a PC which then creates a "mini SMTP" server used to hijack account information, and send bulk email to recipients in the Users' email address book. It can affect the actual machine housing the "Email server platform" or on a local PC which is allowed to connect to the Email Server IP Address on SMTP port 25.
Spamhaus Zen Requires A Manual Delisting Request
This blacklist does support a manual request to remove or delist your IP Address from their database. Please note that removal requests that are submitted without addressing the core problem will likely result in your IP Address or Domain being relisted in that database, which can cause subsequent problems and extended listing periods without release.
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