Custom Mail Tags

How to create custom mail tags. Lets take an example from cf7 website in form-tags topic. I used exactly the same function but in the mail it shows [clocl] instead of time.its not implementing the tag function.

add_action( ‘wpcf7_init’, ‘custom_add_shortcode_clock’ );

function custom_add_shortcode_clock() {
wpcf7_add_shortcode( ‘clock’, ‘custom_clock_shortcode_handler’ ); // “clock” is the type of the form-tag
}

function custom_clock_shortcode_handler( $tag ) {
return date_i18n( get_option( ‘time_format’ ) );
}

Can anyone help?