The Team Cymru Bogons Blacklist is an IP-based blacklist (or blocklist) that identifies bogons, which are invalid IP addresses from unallocated or reserved ranges that should not appear on the public internet.
The Team Cymru Bogons Blacklist is a specialised DNS-based blocklist (DNSBL) that contains bogons. A bogon is an IP address that is not allocated for use on the public internet. This includes IP ranges reserved for private networks (like 192.168.x.x) and other unassigned address spaces. The primary purpose of this blacklist is to enhance network security by filtering out traffic from these invalid addresses, which can sometimes be used in malicious activities like DDoS attacks.
This blocklist is used by network administrators to block traffic at the network perimeter. It is not intended to be used as a filter for email servers, as it does not track IPs based on sending reputation. Technically, when an IP address is checked against the bogons.cymru.com zone, the list responds with an A record of 127.0.0.2 if the IP is a bogon. A TXT record can also be queried to identify the specific bogon prefix the address belongs to.
This bogon blacklist is maintained and operated by Team Cymru. They are an internet security and threat intelligence organization dedicated to making the internet a more secure place. They provide various data feeds and services to help network administrators and security professionals protect their infrastructure. Maintaining a list of bogons is one of the many ways they contribute to a more efficient and secure internet.
A listing on the Team Cymru Bogons Blacklist is fundamentally different from a typical email blacklist or blocklist. You cannot, and do not need to, request delisting. If you are being blocked by this list, it is because your system is using an IP address that is reserved for private networks (such as those starting with 10.x.x.x, 172.16.x.x, or 192.168.x.x) or is otherwise not routed on the public internet.
The problem is not the blacklist itself, but a misconfiguration of the service (like an email server) that is using it. That service is incorrectly checking your private IP instead of your public one. The solution is to contact your network administrator to correct this configuration.
The impact of this blocklist on external email deliverability is very low to none. Since it lists non-routable internet addresses, it will not affect legitimate email sent from a correctly configured server with a valid public IP address. However, if a mail server is misconfigured to use this blacklist, it can cause significant internal problems, such as preventing users on a local network from sending any emails. The issue is a result of an incorrect local setup, not a poor sending reputation.
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