What is Cymru Bogons?
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If you're checking blocklists and your sending IP shows up on Cymru Bogons, that's not a reputation problem. It's a network configuration problem. And there's a meaningful difference.
Team Cymru maintains the Bogons list, which tracks IP addresses that have no business appearing on the public internet. Think unallocated address space, private ranges like 10.x.x.x or 192.168.x.x that somehow turned up on external routes, reserved documentation ranges, and similar addresses that the internet's routing system was never meant to expose. When an IP shows up here, it's not flagged for being spammy. It's flagged for being technically impossible to legitimately own.
The lookup zones are bogons.cymru.com for IPv4 and v6.fullbogons.cymru.com for IPv6.
What actually puts an IP on this list:
- Sending from unallocated address space (nobody officially owns it yet)
- Private or reserved IP ranges appearing on the public internet
- Documentation or example address ranges (like 192.0.2.x) being used for real traffic
- Recently allocated space that hasn't propagated off the bogons list yet
That last point is the one legitimate senders actually run into. When a regional internet registry (like ARIN or RIPE) allocates a fresh block of IPs, there's sometimes a lag before bogons databases update to reflect the change. Your IP is real and assigned to you, but the list hasn't caught up yet. It's frustrating, but it does happen.
So if your IP is genuinely legitimate and recently assigned, the path forward is to contact Team Cymru directly through their website and provide your allocation documentation. They'll update the list. It's not a slow process once you reach them.
If your IP is showing up here and you're not sure why, that's worth a deeper conversation with whoever manages your sending infrastructure or your hosting provider. Using a private range on public traffic, or sending from space that doesn't resolve to a proper allocation, is a signal that something went wrong at a level below the email stack entirely.
For most legitimate senders, this list is essentially invisible. It's aimed at blocklist infrastructure operators and network engineers, not marketing teams. But if you ever do appear on it, don't panic and don't ignore it either. Check whether the IP is genuinely assigned to you, and if it is, get your allocation records in front of Team Cymru.
Not sure where to start? You can check your sending IP against major blocklists with our free blocklist checker, or if this is actively breaking your delivery, our SOS hotline is free and we'll help you figure out what's actually going on.
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