(PHP 4, PHP 5, PHP 7, PHP 8)
checkdnsrr — 给指定的主机（域名）或者IP地址做DNS通信检查
$host
, string $type = "MX"
) : bool
根据不同记录（type）类型查询主机（host）相应的DNS记录。
host
主机（host）可以是一个IP地址也可以是域名。
type
解析记录类型（type）可能是下面这些类型中的任何一个：A，MX，NS，SOA，PTR，CNAME，AAAA，A6， SRV，NAPTR，TXT 或者 ANY。
如果记录能找到，就返回true；如果查找不到该DNS记录或者发生了错误，就返回false。
| 版本 | 说明 |
|---|---|
| 5.3.0 | 这个函数在Windows平台上也可以使用了。 |
| 5.2.4 |
增加了TXT的记录类型。
|
| 5.0.0 |
增加了AAAA的记录类型。
|
I always think you should state the blindingly obvious.
A function that contains checkdnsrr will return false without an internet connection.
So in a production environment you need an active internet connection to return a true result with a valid email address.
$this->_buf - for bulk check cache
function ValidateEmail($email)
{
list($user, $domain) = explode('@', $email);
if (!filter_var($email, FILTER_VALIDATE_EMAIL) !== FALSE)
return 0;
if (isset($this->_buf[$domain]))
return $this->_buf[$domain];
if (checkdnsrr($domain) === FALSE) {
$this->_buf[$domain] = 0;
return 0;
}
$this->_buf[$domain] = 1;
return 1;
}
Important Warning:
You need to add a dot to the end of the host name to make a fully qualified domain name.
To see why, try executing the following pieces of code:
$d1="gmail.con";
$d2="gmail.con.";
$r1=checkdnsrr($d1, "MX");
$r2=checkdnsrr($d2, "MX");
var_dump($r1);
var_dump($r2);
You will see that without the dot it claims that the domain "gmail.con" is valid.
Note that if you time the "checkdnsrr()" calls you will also see it takes longer without the dot because it treats it as a relative domain and does several tries based on the host name it is running on.
NB: in case you're interested, being treated as a relative domain explains what is happening. If your host is "example.com" the relative domain will eventually resolve to "gmail.con.com." which can be looked up, hence it wrongly claims "gmail.con" exists
criffoh at gmail dot com is right. Before you check domain, you must convert to ascii with idn_to_ascii function:
http://us2.php.net/manual/en/function.idn-to-ascii.php .
var_dump(checkdnsrr('?andu.cl', 'A')); // returns false
var_dump(checkdnsrr(idn_to_ascii('?andu.cl'), 'A')); // return true
Is not possible validate domains with '?' for my country.
In my country is possible to register domain using '?' character. For example:
?andu.cl
http://nic.cl/cgi-bin/dom-CL?q=%F1andu
If I use this function to check DNS record, it return false, but the domain already exists:
var_dump(checkdnsrr('?andu.cl', 'A')); // returns false
This is a little code example that will validate an email address in two ways:
- first the general syntax of the string is checked with a regular expression
- then the domain substring (after the '@') is checked using the 'checkdnsrr' function
<?php
function validate_email($email){
$exp = "^[a-z\'0-9]+([._-][a-z\'0-9]+)*@([a-z0-9]+([._-][a-z0-9]+))+$";
if(eregi($exp,$email)){
if(checkdnsrr(array_pop(explode("@",$email)),"MX")){
return true;
}else{
return false;
}
}else{
return false;
}
}
?>