Function node_mail_tick 

pub fn node_mail_tick(
    policy: &WakePolicy,
    seen: &mut MailSeen,
    inbox: &Value,
    door_hint: Option<&str>,
) -> Vec<MailOutcome>

One node-mail tick over a mail.inbox reply: every new message goes to policy.node_mail_to through the pipeline. The first tick only records what is already there.