Audiences and segments
Saved queries over CRM data — live or frozen — that only ever count people who opted in.
Marketing → Audiences.
A segment is a saved query over contacts, accounts or leads. Filters can use any field on those objects, and the count updates as you build.
Live or snapshot. A live segment re-runs every time it is used; a snapshot freezes who was in it.
Only opted-in contacts are counted. A segment should not even count people it may not contact, or every preview overstates your reach and every plan is built on a number that was never real.
Field names are validated against an allow-list, so a saved segment cannot become an injection vector when someone edits it through the API.
Preview a segment to see exactly who is in it before anything is sent.