What are domain monitoring tools (MxToolbox, HetrixTools, etc.)?

Domain monitoring tools track **DNS** health, authentication configuration, and blocklist status for your sending domains. MxToolbox, HetrixTools, **dmarcian**, and similar services provide configuration testing and ongoing monitoring.

Functions include: **DNS record** validation (MX, **SPF**, **DKIM**, **DMARC**), blocklist checking across multiple lists, authentication testing with detailed diagnostics, and alerting when configurations change or problems emerge.

These tools complement **ESP** analytics by focusing on infrastructure health. They catch: **DNS** misconfigurations, expired **DKIM** keys, **SPF record** errors, and blocklist appearances that might not surface in delivery metrics until damage is done.