用javamail发信，提示如下错误，为什么？

[cno]

我用的是sina和163的邮件服务器
smtp.sina.com.cn
163的记不清是smtp.163.com还是smtp.163.net了
反正都试了，都提示如下错误：
javax.mail.NoSuchProviderException: Invalid protocol: null
请问为什么？

[lotofu]

smtp.sina.com.cn???什么意思？
协议和服务器混为一谈？！！！！！

[cno]

那怎么会出现这种情况呢？

[takecare]

telnet smtp.sina.com.cn 25

ehlo或helo看看该服务器支持什么样的东东

[cno]

看了，是下面这些，什么意思啊？
250-sina.com
250-AUTH=LOGIN
250-AUTH LOGIN
250-PIPELINING
250 8BITMIME
250 sina.com

[lotofu]

Properties props = System.getProperties();
props.put("mail.host", host);
props.put("mail.transport.protocol", "smtp");

[cno]

Properties properties = System.getProperties();
properties.put("mail.smtp.host","smtp.sina.com.cn");
properties.put("mail.transport.protocol", "smtp");
properties.put("mail.smtp.auth","true");
Session session = Session.getInstance(properties,
new Authenticator() {
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication("myusername","mypassword");
}
});

try
{
MimeMessage message = new MimeMessage(session);
message.setFrom(new InternetAddress(strFrom));

InternetAddress[] toadd = InternetAddress.parse(strEmail);
message.setRecipients(Message.RecipientType.TO,toadd);

message.setSubject(strSubject);
message.setText(strFullMailText);

Transport transport = session.getTransport();
message.saveChanges();
transport.send(message,message.getAllRecipients());
transport.close();

}
catch (AddressException e)
{
System.out.println("There was an error parsing the addresses.");
System.out.println(e.getMessage());
}
catch (SendFailedException e)
{
System.out.println("There was an error sending the message.");
System.out.println(e.getMessage());
}
catch (MessagingException e)
{
System.out.println("There was an unexpected eorror.");
System.out.println(e);
}
楼上的，这是我的程序，照你的方法改了，好了
什么错误都不提示了
可就是没有收到信，见鬼了

[myxd]

如果你用的TOMCAT。你可以看看tomcat代的例子。能简单