double get_rate() const { return rate_; }
MailboxImpl* get_mailbox() const { return mbox_; }
long get_mailbox_id() const { return mbox_id_; }
double get_rate() const { return rate_; }
MailboxImpl* get_mailbox() const { return mbox_; }
long get_mailbox_id() const { return mbox_id_; }