最近在測試公司內部系統自動傳送郵件功能時，一直在報錯：

javax.mail.SendFailedException: Sending failed;
  nested exception is: 
	javax.mail.MessagingException: Could not connect to SMTP host: 10.1.1.195, port: 25;
  nested exception is: 
	java.net.SocketException: Network is unreachable: connect
	at javax.mail.Transport.send0(Transport.java:219)
	at javax.mail.Transport.send(Transport.java:81)
	at com.gree.util.MailUtil.sendMessage(MailUtil.java:241)
	at com.gree.util.MailUtil.sendTest(MailUtil.java:1112)
	at com.gree.util.MailUtil.main(MailUtil.java:1120)</span>
 

在同事的電腦上同樣的專案同樣的程式碼都沒問題，所以排除了伺服器錯誤的問題，通過telnet測試埠也沒問題，也可以ping通，最後發現原來是tomcat伺服器缺少某些啟動引數。。解決方法：在tomcat配置中加入該引數
Servers->雙擊Tomcat->Open launch configuration->Arguments->在VM arguments輸入框最後新增下面這句：

-Djava.net.preferIPv4Stack=true</span>

然後在main函式開頭新增下面這句：

System.setProperty("java.net.preferIPv4Stack", "true");</span>