在Linux下使用JavaMail发送邮件报错：javax.mail.MessagingException: Unknown SMTP host:

使用JavaMail发送邮件， 在Windows上测试都是OK的，但发布Linux上，测试后报Unknown SMTP host异常。

异常信息如下：

javax.mail.MessagingException: Unknown SMTP host: smtp.126.com;

nested exception is:

java.net.UnknownHostException: smtp.126.com

at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1704)

at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:525)

at javax.mail.Service.connect(Service.java:297)

at javax.mail.Service.connect(Service.java:156)

at javax.mail.Service.connect(Service.java:105)

at javax.mail.Transport.send0(Transport.java:168)

at javax.mail.Transport.send(Transport.java:98)

at com.utvchina.cas.util.MailSender.sendHtmlMail(MailSender.java:107)

at com.utvchina.cas.util.MailSender.send(MailSender.java:133)

at com.utvchina.cas.util.VerificationInfo.send(VerificationInfo.java:64)

at com.utvchina.cas.action.RegisterAction.save(RegisterAction.java:124)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

at java.lang.reflect.Method.invoke(Method.java:597)

at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:441)

at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:280)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:243)

at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:165)

at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:252)

at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)

at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)

at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)

at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:179)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:235)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:130)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)

at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:165)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:179)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)

at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)

at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:488)

at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)

at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)

at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)

at com.github.inspektr.common.web.ClientInfoThreadLocalFilter.doFilter(ClientInfoThreadLocalFilter.java:46)

at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)

at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)

at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)

at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)

at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)

at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:440)

at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:199)

at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)

at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)

at org.mortbay.jetty.Server.handle(Server.java:326)

at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)

at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:943)

at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)

at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)

at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)

at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)

at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

Caused by: java.net.UnknownHostException: smtp.126.com

at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:177)

at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)

at java.net.Socket.connect(Socket.java:529)

at java.net.Socket.connect(Socket.java:478)

at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:284)

at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:227)

at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1672)

... 82 more

解决方法：

这个问题主要是软防火墙(iptables)中邮件发送端口未对外开放。

邮件端口为25

修改iptables即可，步骤如下：

1、修改/etc/sysconfig/iptables文件，增加如下一行：

　　-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 25 -j ACCEPT

　

2、重启防火墙，这里有两种方式重启防火墙

　　a) 重启后生效

　　开启： chkconfig iptables on

　　关闭： chkconfig iptables off

　　b) 即时生效，重启后失效

　　开启： service iptables start

　　关闭： service iptables stop

还有一个可能的原因就是：DNS未配置或配置不成功(可ping测试一下)