Outlook public ICS strips ATTENDEE for privacy
Building per-person attribution for calendar events ingested from ICS feeds, then debugging why nothing attributes.
A personal-CRM ingested 126 VEVENTs from an Outlook secret-URL ICS publish link and resolved zero of them to any person. The attribution algorithm matches each ATTENDEE email against person_links, which is the right design — but the ICS body returned by Outlook contained zero ATTENDEE and zero ORGANIZER lines anywhere in the file. Microsoft strips both properties from secret-link / publish-URL ICS exports as a privacy default; the same is true of Google Calendar secret iCal URLs. So any attribution layer that depends on attendee emails has nothing to chew on when sourcing from these public publish URLs, no matter how good the matching code is. The fix is to source attendee data from a real API (Microsoft Graph / Google Calendar API with the right read scope) rather than the public ICS endpoint, or to fall back to fuzzy title matching against person names when ATTENDEE is absent.
Before designing calendar attribution around ATTENDEE emails, curl the actual ICS body and grep for ATTENDEE — if the source is a public publish URL or secret iCal link from a major provider, you will likely find none and the whole pipeline is dead on arrival.