When Odoo receives an incoming message that includes a CC that is not a contact, The resulting notification to the followers ( including me) is striped of this new individual e-mail address.
Leaving me no way to even add them as a follower manually to become part of the "thread".
I thought this information would be logged somewhere ( developer >manage messages) as the cc should be “ingested” initially by Odoo from the original message, but I can’t find it anywhere.