In order to deliver important e-mails without unnecessary delay, some priority delivery methods with a whitelist, which includes trusted sending Mail Transfer Agents (MTAs), are proposed so far. However, most conventional methods have some problems with a large sized whitelist such as performance degradation, delivery failure, and so on. To alleviate these problems, we proposed a priority delivery system (Prototype system) by using a layer 3 switch (L3SW) with policy based routing (PBR) function. By updating PBR entries dynamically, prototype system implements a large sized whitelist without performance degradation. In this paper, we investigated the case many sending MTAs same time send Email performance of the prototype system. we also describe prototype system improvements.