That will not be practical because every field require individual type of validation and sanitize.

You can easily capture id from url and add that in post meta. Use code like

add_action( 'fep_action_message_after_send', function( $message_id, $message, $inserted_message ){
    wp_parse_str( $_SERVER['HTTP_REFERER'], $referrer );
    $id = !empty( $referrer['id'] ) ? absint($referrer['id']) : 0; //Change id with your parameter
    //here if require check some validation
    add_post_meta( $message_id, '_your_custom_meta_key', $id );
}, 10, 3 );