Failed to send out e-mail

java.net.ConnectException: Connection refused (Connection refused)
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:606)
at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:666)
at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:286)
at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:205)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1900)
Caused: javax.mail.MessagingException: Could not connect to SMTP host: smtp.gmail.com, port: 465;
  nested exception is:
java.net.ConnectException: Connection refused (Connection refused)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1934)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:638)
at javax.mail.Service.connect(Service.java:317)
at javax.mail.Service.connect(Service.java:176)
at javax.mail.Service.connect(Service.java:125)
at javax.mail.Transport.send0(Transport.java:194)
at javax.mail.Transport.send(Transport.java:124)
at hudson.tasks.Mailer$DescriptorImpl.doSendTestMail(Mailer.java:673)
at java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:627)
at org.kohsuke.stapler.Function$MethodFunction.invoke(Function.java:396)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:408)
at org.kohsuke.stapler.interceptor.RequirePOST$Processor.invoke(RequirePOST.java:77)
at org.kohsuke.stapler.PreInvokeInterceptedFunction.invoke(PreInvokeInterceptedFunction.java:26)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:212)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:145)
at org.kohsuke.stapler.MetaClass$11.doDispatch(MetaClass.java:535)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:747)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:878)
at org.kohsuke.stapler.MetaClass$4.doDispatch(MetaClass.java:280)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:747)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:878)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:676)
at org.kohsuke.stapler.Stapler.service(Stapler.java:238)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:154)
at jenkins.telemetry.impl.UserLanguages$AcceptLanguageFilter.doFilter(UserLanguages.java:128)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:151)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:157)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:99)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:117)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.BasicHeaderProcessor.doFilter(BasicHeaderProcessor.java:93)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:67)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:90)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:171)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:82)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:645)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:609)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:810)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1506)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)