故障現象：
Ex03升級至ex07後新郵箱用戶無法發送郵件至ex03用戶郵箱
Ex07郵件隊列顯示如下錯誤信息：
"451 5.7.3 cannot achieve exchange server authentication." Attempted failover to alternate host,but that did not succeed.Either there are no alternate hosts,or delivery failed to all alternate hosts.
故障排除：
經檢查，ex07至ex03雙向郵件路由均正常
經搜索相關資料，發現可能系cisco防火牆的smtp篩選功能導致，關閉smtp篩選後故障消失
相關資料：
http://social.technet.microsoft.com/Forums/en-US/exchangesvrtransport/thread/8a22d871-c596-412a-90ee-e3e8933e6788