True when the note carried an explicit, user-curated recipient set (either
platform-resolved recipients or a connector-resolved access-contact
constraint). When true and every list is empty, the connector should
surface a deliveryError ("no deliverable recipients") rather than
silently skipping — the user asked to send to specific people and none
could be addressed. When false (a plain reply-all), an empty result just
means the conversation had no other participants.
Outbound recipient lists for a reply, split by header role.
bccrecipients MUST be addressed privately (a separate Bcc header / bccRecipients field) so they are never exposed to the To/Cc recipients.