为什么后台用Java发邮件，在本地可以，部署到vps上就不行了？

本地ubuntu , vps是centOS
到底是哪里出问题了呢？
试了456端口和25端口都不行……服务器是tomcat
另，服务器上用Python写脚本是可以发邮件的= =！

package util;

import javax.mail.*;
import javax.mail.internet.*;
import java.util.*;

public class MailSender {

	public void postMail(String recipients[], String subject, String text) {
		// Set the host smtp address
		ResourceBundle rb = ResourceBundle.getBundle("mail");
		String host = rb.getString("smtp");
		int port = 25;
		String from = rb.getString("from");
		// Get system properties
		Properties props = new Properties();
		// Setup mail server
		props.setProperty("mail.smtp.host", host);
		 props.put("mail.smtp.auth","true");
		 props.put("mail.smtp.port", port);
		// Get the default Session object.props.put("mail.smtp.auth", "true");
		Session session = Session.getDefaultInstance(props,
				new javax.mail.Authenticator() {
					protected PasswordAuthentication getPasswordAuthentication() {
						ResourceBundle rb = ResourceBundle.getBundle("mail");
						String username = rb.getString("username");
						String password = rb.getString("password");
						return new PasswordAuthentication(username, password);
					}
				});

		try {
			// Create a default MimeMessage object.
			MimeMessage message = new MimeMessage(session);

			// Set the RFC 822 "From" header field using the
			// value of the InternetAddress.getLocalAddress method.
			message.setFrom(new InternetAddress(from));

			// Add the given addresses to the specified recipient type.
			StringBuilder sb = new StringBuilder();
			for (String s : recipients) {
				sb.append(" ");
				sb.append(s);
			}
			message.setRecipients(Message.RecipientType.TO,
					InternetAddress.parse(sb.toString()));

			message.setRecipients(Message.RecipientType.TO,
					InternetAddress.parse(sb.toString()));
			message.setSubject(MimeUtility.encodeText(subject));
			message.setContent(text, "text/html;charset=utf8");
			Date date = new Date();
			message.setSentDate(date);

			Transport.send(message);

			System.out.println("Done");
		} catch (Exception e) {
			e.printStackTrace();
			LogDetail.logexception(e);
		}
	}
}