# Using File Transport

`Zend_Mail_Transport_File` is useful in a development environment or for testing purposes. Instead of sending any real emails it simply dumps the email's body and headers to a file in the filesystem. Like the other transports, it may be configured using `Zend_Application_Resource_Mail`, or by passing an instance to the `send()` method of a `Zend_Mail` instance.

The transport has two optional parameters that can be passed to the constructor or via `setOptions()` method. The path option specifies the base path where new files are saved. If nothing is set, the transport uses the default system directory for temporary files. The second parameter, callback, defines what PHP callback should be used to generate a filename. As an example, assume we need to use the recipient's email plus some hash as the filename:

    function recipientFilename($transport)
    {
        return $transport->recipients . '_' . mt_rand() . '.tmp';
    }

    $mail = new Zend_Mail();
    $mail->addTo('somebody@example.com', 'Some Recipient');
    // build message...
    $tr = new Zend_Mail_Transport_File(array('callback' => 'recipientFilename'));
    $mail->send($tr);

The resulting file will be something like `somebody@example.com_1493362665.tmp`

## Include randomness in filename generation

When generating filenames, you should inject some sort of randomness into the generation to ensure that the filenames are unique. This is especially important on servers where you may expect high load, as it will ensure that despite a number of requests coming in during the same second or millisecond, the filename will still be unique.