jenkins 配置发送邮件，发送测试邮件，邮件发送失败：

Failed to send out e-mail

javax.mail.MessagingException: Could not connect to SMTP host: localhost, port: 25;
  nested exception is:
	java.net.ConnectException: Connection refused: connect

	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:295)

	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:581)

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

	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

	at java.lang.reflect.Method.invoke(Method.java:497)

	at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:335)

	at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:175)

jenkins 发送邮件失败