Blocklist monitoring 101

DNS blocklists are real-time databases of IP addresses and domains known to send spam. Being listed can severely impact email deliverability.

Major blocklists

**Spamhaus**: Industry standard, most widely used
**SURBL**: Focuses on domains in spam emails
**Barracuda**: Real-time reputation database
**SORBS**: Spam and open relay blocker
**SpamCop**: User-reported spam tracker

How listings happen

Spam complaints from recipients
Spam trap hits (sending to honeypot addresses)
Compromised accounts sending spam
Open relay or proxy detection
Poor list hygiene (high bounce rates)

Prevention strategies

Implement proper email authentication (SPF, DKIM, DMARC)
Use confirmed opt-in for all subscriptions
Remove hard bounces immediately
Monitor engagement and remove inactive subscribers
Never purchase email lists
Use dedicated IPs for high-volume sending

Delisting process

Each blocklist has its own removal procedure: 1. Identify the reason for listing 2. Fix the underlying issue 3. Submit delisting request with details 4. Implement monitoring to prevent relisting

Most listings are time-based and auto-expire if no new reports occur.