Exchange 2010 Hub Transport Server 出現 Event ID 1021 警告訊息

Exchange 2010系統上線一段時間後，在信件流量巔峰期間時有收信緩慢現象發生，檢查後發現信件會卡在外部SMTP郵件主機上的郵件佇列中，而無法正常傳送給Exchange 2010 Hub Transport Server，在Exchange 2010 Hub Transport Server上會出現Event ID 1021 警告訊息

問題原因：
新建立的Receive Connector有啟用針對同一個來源伺服器的連線限制功能，預設值如下圖：

 

所以當信件流量過大而超過此連線限制時，Exchange 2010 Hub Transport Server就會拒絕外部SMTP郵件主機的連線要求，而導致信件無法正常傳送問題發生。

參數設定說明如下：

• The MaxInboundConnection parameter specifies the maximum number of inbound connections that this Receive connector serves at the same time. The default value is 5000. The valid input range for this parameter is from 1 through 2147483647. To disable the inbound connection limit on a Receive connector, enter a value of unlimited.
• The MaxInboundConnectionPerSource parameter specifies the maximum number of inbound connections that this Receive connector serves at the same time from a single IP address. The default value is 100. The valid input range for this parameter is from 1 through 10000. To disable the inbound connection per source limit on a Receive connector, enter a value of unlimited.
• The MaxInboundConnectionPercentagePerSource parameter specifies the maximum number of connections that a Receive connector serves at the same time from a single IP address. The value is expressed as the percentage of available remaining connections on a Receive connector. Enter the value as an integer without the percent (%) character. The default value is 2 percent. The valid input range for this parameter is from 1 through 100.

解決方法：
可以使用Exchange 2010 Management Shell 指令來針對Receive Connector進行連線限制的調整，指令範例如下：

Set-ReceiveConnector -Identity "Server Name\Receive Connector Name" -MaxInboundConnectionPerSource unlimited -MaxInboundConnectionPercentagePerSource 100