Heartbeat alert

The heartbeat check flags any active domain with no reports received in the last N days (configurable). For a domain that has never received a report at all, it falls back to comparing against the domain's onboarding date instead, so a brand-new domain doesn't false-positive on day one just because reports haven't arrived yet.

A heartbeat firing usually means either your IMAP polling has broken, or a major receiver has stopped sending you reports — worth checking the domain page's ingestion-health indicator first.