Breaking contract change: message.received includes required disposition and reason
fields. Update your webhook payload types and fixtures. Check disposition === "delivered"
before treating an email as delivered; reason is null for delivered messages.
Email missing a receipt verdict is quarantined with reason verdict_missing. A quarantined
email still produces the organization webhook with its body. Isolated malware produces no
organization received webhook.
The event describes the receipt decision when it is committed. Mailbox content screening can subsequently hold a message; follow mailbox events and the quarantine API for those holds.