checkdnsrr

    (PHP 4, PHP 5, PHP 7, PHP 8)

    checkdnsrr — Check DNS records corresponding to a given Internet host name or IP address

    Description

    checkdnsrr(string $hostname, string $type = "MX"): bool

    Searches DNS for records of type type corresponding to hostname.

    Parameters

    hostname

    hostname may either be the IP address in dotted-quad notation or the host name.

    type

    type may be any one of: A, MX, NS, SOA, PTR, CNAME, AAAA, A6, SRV, NAPTR, TXT or ANY.

    Return Values

    Returns true if any records are found; returns false if no records were found or if an error occurred.

    Notes

    Note:

    For compatibility with Windows before this was implemented, then try the » PEAR class » Net_DNS.

    See Also

    • dns_get_record() - Fetch DNS Resource Records associated with a hostname
    • getmxrr() - Get MX records corresponding to a given Internet host name
    • gethostbyaddr() - Get the Internet host name corresponding to a given IP address
    • gethostbyname() - Get the IPv4 address corresponding to a given Internet host name
    • gethostbynamel() - Get a list of IPv4 addresses corresponding to a given Internet host name
    • the named(8) manual page

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    User Contributed Notes 4 notes

    up
    34
    Krisztin Ferenczi
    11 years ago
    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('ñandu.cl', 'A')); // returns false
    var_dump(checkdnsrr(idn_to_ascii('ñandu.cl'), 'A')); // return true
    up
    16
    Martin
    8 years ago
    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
    up
    1
    n at zay dot uk
    3 years ago
    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.
    up
    -1
    Patrick
    19 years ago
    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;

    }
    }

    ?>
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