Ověření „platnosti“ e-mailové adresy v PHP

Dnes jsem se probíral sbírkou kódů, které jsem si zkopíroval z netu, a našel jsem tuto zajímavou funkci.

Nejsem jejím autorem a původní zdroj jsem si nepoznamenal.

function CheckMail($Email,$Debug=false)   
{   
    global $HTTP_HOST;   
    $Return =array();    
    // Variable for return.   
    // $Return[0] : [true|false]   
    // $Return[1] : Processing result save.   

    if (!eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", $Email))
{   
        $Return[0]=false;   
        $Return[1]="${Email} is E-Mail form that is not right.";   
        if ($Debug) echo "Error : {$Email} is E-Mail form that is not right.<br>";           
        return $Return;   
    }   
    else if ($Debug) echo "Confirmation : {$Email} is E-Mail form that is not right.<br>";   

    // $Username : lsm   
    // $Domain : xxx.com   
    // list function reference : http://www.php.net/manual/en/function.list.php   
    // split function reference : http://www.php.net/manual/en/function.split.php   
    list ( $Username, $Domain ) = split ("@",$Email);   

    // That MX(mail exchanger) record exists in domain check .   
    // checkdnsrr function reference : http://www.php.net/manual/en/function.checkdnsrr.php   
    if ( checkdnsrr ( $Domain, "MX" ) )  {   
        if($Debug) echo "Confirmation : MX record about {$Domain} exists.<br>";   
        // If MX record exists, save MX record address.   
        // getmxrr function reference : http://www.php.net/manual/en/function.getmxrr.php   
        if ( getmxrr ($Domain, $MXHost))  {   
      if($Debug) {   
                echo "Confirmation : Is confirming address by MX LOOKUP.<br>";   
              for ( $i = 0,$j = 1; $i < count ( $MXHost ); $i++,$j++ ) {   
            echo "????????Result($j) - $MXHost[$i]
<BR>";    
        }   
            }   
        }   
        // Getmxrr function does to store MX record address about $Domain in arrangement form to $MXHost.   
        // $ConnectAddress socket connection address.   
        $ConnectAddress = $MXHost[0];   
    }   
    else {   
        // If there is no MX record simply @ to next time address socket connection do .   
        $ConnectAddress = $Domain;           
        if ($Debug) echo "Confirmation : MX record about {$Domain} does not exist.<br>";   
    }   

    // fsockopen function reference : http://www.php.net/manual/en/function.fsockopen.php   
    $Connect = fsockopen ( $ConnectAddress, 25 );   

    // Success in socket connection   
    if ($Connect)     
    {   
        if ($Debug) echo "Connection succeeded to {$ConnectAddress} SMTP.<br>";   
        // Judgment is that service is preparing though begin by 220 getting string after connection .   
        // fgets function reference : http://www.php.net/manual/en/function.fgets.php   
        if ( ereg ( "^220", $Out = fgets ( $Connect, 1024 ) ) ) {   

            // Inform client's reaching to server who connect.   
            fputs ( $Connect, "HELO $HTTP_HOST\r\n" );   
                if ($Debug) echo "Run : HELO $HTTP_HOST<br>";   
            $Out = fgets ( $Connect, 1024 ); // Receive server's answering cord.   

            // Inform sender's address to server.   
            fputs ( $Connect, "MAIL FROM: <{$Email}>\r\n" );   
                if ($Debug) echo "Run : MAIL FROM: <{$Email}><br>";   
            $From = fgets ( $Connect, 1024 ); // Receive server's answering cord.   

            // Inform listener's address to server.   
            fputs ( $Connect, "RCPT TO: <{$Email}>\r\n" );   
                if ($Debug) echo "Run : RCPT TO: <{$Email}><br>";   
            $To = fgets ( $Connect, 1024 ); // Receive server's answering cord.   

            // Finish connection.   
            fputs ( $Connect, "QUIT\r\n");   
                if ($Debug) echo "Run : QUIT<br>";   

            fclose($Connect);   

                // Server's answering cord about MAIL and TO command checks.   
                // Server about listener's address reacts to 550 codes if there does not exist    
                // checking that mailbox is in own E-Mail account.   
                if ( !ereg ( "^250", $From ) || !ereg ( "^250", $To )) {   
                    $Return[0]=false;   
                    $Return[1]="${Email} is address done not admit in E-Mail server.";   
                    if ($Debug) echo "{$Email} is address done not admit in E-Mail server.<br>";   
                    return $Return;   
                }   
        }   
    }   
    // Failure in socket connection   
    else {   
        $Return[0]=false;   
        $Return[1]="Can not connect E-Mail server ({$ConnectAddress}).";   
        if ($Debug) echo "Can not connect E-Mail server ({$ConnectAddress}).<br>";   
        return $Return;   
    }   
    $Return[0]=true;   
    $Return[1]="{$Email} is E-Mail address that there is no any problem.";   
    return $Return;   
}