Create a new email broadcast. Broadcasts are created in DRAFT status — creating one does not send it. To send it, create a send action for the broadcast (POST /emails/broadcasts/{broadcast_id}/send_actions): omit send_at to send now, or pass a future send_at to schedule. (Alternatively, the legacy inline path accepts recipients with send_immediately=true, or send_at/send_at_local_time/time_zone to schedule.) When accessing the API through an OAuth connection from a third-party platform, this endpoint is restricted to trusted developer platforms. If you are using your own API key, you can send emails directly from your account. Prefer a verified sending address for from_email and reply_to_email: an unverified custom domain hurts deliverability, while the shared workspace-default domain is a safe fallback. List addresses (with their verification status) via GET /workspaces/{workspace_id}/emails/addresses.