// We must handle mbox subscription only if it is not MPSC mbox.
if( mbox_type_t::multi_producer_single_consumer != mbox->type() )
    {
        // If there was no subscription for that mbox
        // then new subscription in the mbox must be created.
        if( !is_known_mbox_msg_pair( m_events, ins_result.first ) )
            {
                try
                    {
                        mbox->subscribe_event_handler( msg_type, owner() );
                    }
                catch( ... )
                    {
                        // Rollback agent's subscription.
                        m_events.erase( ins_result.first );
                        throw;
                    }
            }
    }