1、錯誤描寫敘述

DEBUG: setDebug: JavaMail version 1.3.3
DEBUG: getProvider() returning javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Sun Microsystems, Inc]
DEBUG SMTP: useEhlo true, useAuth true
DEBUG SMTP: trying to connect to host "localhost", port 25, isSSL false
Exception in thread "main" 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:1227)
	at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:322)
	at javax.mail.Service.connect(Service.java:236)
	at javax.mail.Service.connect(Service.java:137)
	at com.you.mail.model.SendMessage.sendMessage(SendMessage.java:70)
	at com.you.mail.model.SendMessage.main(SendMessage.java:89)

從報錯可知，無法連接SMTP服務主機

3、解決的方法

配置正確的SMTP服務主機。保證服務連接上

String server = "smtp.163.com";
String username = "";
String password = "";
		
Transport transport = session.getTransport();
transport.connect(server, username, password);
transport.sendMessage(message, message.getRecipients(Message.RecipientType.TO));
transport.close();

Could not connect to SMTP host: localhost, port: 25;