IP blacklist checking on aliases

In addition to spam scoring, you can enable IP blacklist checking (DNSBL) on individual aliases. When enabled, the sending server's IP address is checked against well-known blacklist databases before the email is accepted.

How it works

1. An email arrives at your alias
2. Cleanbox extracts the sending server's IP address from the SMTP connection
3. The IP is queried against selected DNSBL providers
4. If the IP is listed on any selected blacklist, the email is rejected
5. If the IP is clean, processing continues normally (spam scoring, filters, etc.)

Enabling IP blacklist checking

1. Go to Aliases → click an alias
2. Scroll to the IP Blacklist Check section
3. Select which blacklist providers to check against
4. Click Save blacklist settings

Available blacklist providers

Cleanbox supports checking against several well-known DNSBL providers, including Spamhaus, Barracuda, and SpamCop. Each provider maintains its own database of IP addresses known to send spam.

False positives

Occasionally, a legitimate sender's IP may appear on a blacklist — for example, if their email provider's IP was previously used by a spammer. If you notice legitimate email being rejected:

• Check the message log for rejected messages — the rejection reason indicates which blacklist triggered
• Whitelist the contact — Set the contact state to whitelisted. Whitelisted contacts bypass spam checks, which includes IP blacklist checking.
• Reduce the number of selected providers to only the most reliable ones

Aliases vs Relay blacklists

Relay addresses also support IP blacklist checking, but the configuration is per-domain (on the relay settings page) rather than per-alias. The available providers and behavior are the same.