不幸的是，没有标准方法可以为任意电子邮件地址识别正确的外发SMTP服务器，假设您要做的是让用户指定一个电子邮件地址/密码，然后使用该帐户发送邮件。

这就是电子邮件客户端（例如Thunderbird，Outlook等）通常需要用户的原因手动配置传出SMTP服务器名称/端口。你可以通过识别一些流行的ISP（谷歌，雅虎等）并预先配置正确的值来协助这个过程，但是没有通用的方法可以自动完成。

I made a simple application to send e-mails using Java API and have a question:

Is there any way to find out the SMTP host knowing the e-mail address of the one who will login to send an e-mail? And also the port?

For example, if the sender's e-mail address is sender@gmail.com, the SMTP host is smtp.gmail.com and the port 465. If the sender's e-mail address is sender@yahoo.com, the SMTP host is smtp.yahoomail.com and the port 25.

Supposing I don't know this, is there any way to find this information using Java API classes? Please note that I'm new to java :)

Thanks in advance,

Andreea

---

Thanks for your answers. I've tried to do the following:

    public static String getMXRecordsForEmailAddress(String eMailAddress) { 

            String returnValue = null; 

            try { 
                String hostName = getHostNameFromEmailAddress(eMailAddress); 
                Record[] records = new Lookup(hostName, Type.MX).run(); 
                if (records == null) { 
             throw new RuntimeException("No MX records found for domain " + hostName + ".");
 } 

                // return first entry (not the best solution) 
                if (records.length > 0) { 
                        MXRecord mx = (MXRecord) records[0]; 
                        returnValue = mx.getTarget().toString(); 
                } 
            } catch (TextParseException e) { 
                throw new RuntimeException(e); 
            } 

            System.out.println("return value = "+returnValue);
            return returnValue; 
        } 

But, regardless of the value of hostName (eg. gmail.com, yahoo.com ) Record[] records = new Lookup(hostName, Type.MX).run(); always return null.

I'm pretty sure that I missed something, but I don't know what. Will you please help me with this? Can you tell me what I'm doing wrong?

Thank you verry much,

Andreea

Unfortunately, there's no standard way to identify the correct outgoing SMTP server for an arbitrary email address, assuming what you're trying to do is let the user specify an email address/password and then send the mail using that account.

That's why email clients (e.g. Thunderbird, Outlook, etc.) generally require the user to configure the outgoing SMTP server name/port manually. You could assist in that process by recognizing a few popular ISPs (Google, Yahoo, etc.) and pre-configuring the proper values, but there's no general-purpose way to do that automatically.