Outgoing mail
A successful `202` means the configured Resend API accepted the request. It is not a delivery receipt. Later provider events may update accepted, delivered, delayed, bounced, complained, failed, or suppressed status.
Inbound delivery
Inbound delivery to Helios Post is handled by the configured Resend inbound webhook. The webhook signature, event timestamp, payload shape, attachment limits, duplicate event ID, recipient routing, and owned address are validated server-side before a message is persisted.
Webhook availability
Mail does not currently publish a customer-configurable outbound webhook subscription API. The inbound Resend endpoint is a provider integration, not a customer webhook URL. Do not send events to it directly or disable signature checks.
Reconcile status
Use message status values as operational signals, not proof that a recipient viewed or acted on an email. Account for delayed provider events and duplicate delivery notifications.