<?php if ( $post->post_type == 'post' && $post->post_status == 'publish' ) {
		$attachments = get_posts( array(
			'post_type' => 'attachment',
			'posts_per_page' => -1,
			'post_parent' => $post->ID,
			'exclude'     => get_post_thumbnail_id()
		) );

		if ( $attachments ) {
			foreach ( $attachments as $attachment ) {
				$class = "post-attachment mime-" . sanitize_title( $attachment->post_mime_type );
				$thumbimg = wp_get_attachment_link( $attachment->ID, 'thumbnail-size', true );
				echo '<li class="' . $class . ' data-design-thumbnail">' . $thumbimg . '</li>';
			}
			
		}
	}
?>