两种获取SMTP服务器的方式

通过开源软件dnsjava来获取

try{
			Lookup lookup=new Lookup("foxmail.com",Type.MX);
			lookup.setResolver(new SimpleResolver("172.19.5.35"));
			lookup.run();
			System.out.println(lookup.getErrorString());
			if(lookup.getResult()!=Lookup.SUCCESSFUL){
				System.out.println("ERROR!");
			}else{
				Record[] result=lookup.getAnswers();
				for(int i=0;i<result.length;i++){
					String host=result[i].getAdditionalName().toString();
					System.out.println(host);
				}
			}
		}catch(TextParseException e){
			e.printStackTrace();
		}

通过JNDI来获取

private String[] getSMTPServerByJNDI(String host) throws Exception {
		Properties jndiEnvironmentProperties = new Properties();
		jndiEnvironmentProperties.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
		DirContext initialDirContext = new InitialDirContext(jndiEnvironmentProperties);
		Attributes attributes = initialDirContext.getAttributes(host, new String[] {"MX"});
		Attribute attribute = attributes.get("MX");
		String[] servers = new String[attribute.size()];
		for (int i = 0; i < attribute.size(); i++) {
			servers[i] = attribute.get(i).toString();
			servers[i]=servers[i].substring(servers[i].indexOf(" ") + 1, servers[i].length() -1);
			System.out.println(servers[i]);
		}
		return servers;
	}