How do they detect blacklist listings?

Monitoring tools query blocklists programmatically, checking your IPs and domains against known lists regularly. When a listing appears, alerts notify you immediately so you can investigate and remediate.

Checking methods: **DNS**-based queries to DNSBL lists return positive results for listed addresses, web **API** queries to blocklist providers, and aggregated services checking multiple lists simultaneously.

Early detection matters because listings damage delivery immediately. Tools checking frequently (hourly or more often) catch listings before widespread impact. They also track delisting to confirm remediation success and monitor for re-listing.