使用 JAVA API 查找知道电子邮件地址的 SMTP 主机和端口

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; 
} 

但是，无论 hostName 的值如何(例如 gmail.com、yahoo.com )Record[] records = new Lookup(hostName, Type.MX).run(); 总是返回 null.