PHP: Sending an Email Attachment

Here’s my adapted version of sending an email attachment and allowing HTML and plain encodings.

emailFile(array(
    'to' => 'your@email.com',
    'from' => 'my@email.com',
    'subject' => 'Some Subject',
    'message' => '<b>Hello!</b>',
    'plain ' => 'Get a new email client!',
    'file' => '/path/to/file'
));

/**
 * Sends an email in html and plain encodings with a file attachment.
 *
 * @param array $args Arguments associative array
 *      'to' (string)
 *      'from' (string)
 *      'subject' (optional string)
 *      'message' (HTML string)
 *      'plain' (optional plain string)
 *      'file' (optional file path of the attachment)
 * @see http://webcheatsheet.com/php/send_email_text_html_attachment.php
 */
function emailFile($args) {
    $to = set_default($args['to']);
    $from = set_default($args['from']);
    $subject = set_default($args['subject'], '');
    $message = set_default($args['message'], '');
    $plain = set_default($args['plain'], '');
    $file = set_default($args['file']);

    // MIME
    $random_hash = md5(date('r', time()));
    $boundaryMixed = 'PHP-mixed-' . $random_hash;
    $boundaryAlt = 'PHP-alt-' . $random_hash;
    $charset = 'UTF-8';
    $bits = '8bit';

    // Headers
    $headers = "MIME-Version: 1.0";
    $headers .= "Reply-To: $to\r\n";
    if ($from !== NULL) {
        $headers .= "From: $from\r\n";
    }
    $headers .= "Content-Type: multipart/mixed; boundary=$boundaryMixed";
    if ($file !== NULL) {
        $info = pathinfo($file);
        $filename = $info['filename'];
        $extension = $info['extension'];
        $contents = @file_get_contents($file);
        if ($contents === FALSE) {
            throw new Exception("File contents of '$file' could not be read");
        }
        $chunks = chunk_split(base64_encode($contents));
        $attachment = <<<EOT
--$boundaryMixed
Content-Type: application/$extension; name=$filename.$extension
Content-Transfer-Encoding: base64
Content-Disposition: attachment

$chunks
EOT;
    } else {
        $attachment = '';
    }

    $body = <<<EOT
--$boundaryMixed
Content-Type: multipart/alternative; boundary=$boundaryAlt

--$boundaryAlt
Content-Type: text/plain; charset="$charset"
Content-Transfer-Encoding: $bits

$plain

--$boundaryAlt
Content-Type: text/html; charset="$charset"
Content-Transfer-Encoding: $bits

$message
--$boundaryAlt--

$attachment

--$boundaryMixed--
EOT;

    $result = @mail($to, $subject, $body, $headers);
    return $result;
}

function set_default(&$var, $default = NULL) {
    return isset($var) ? $var : $default;
}