alert_netadmin_low_blog_space

/**
 * Send email to super admin when the blog's available space is less than 200MB
 */
function ls_blog_space_mail() {
    $space_left = round( get_upload_space_available() / 1024 / 1024 );
    if ( $space_left < 200 ) {
	$message = 'Site ' . get_site_url() . ' has only ' . $space_left . 'MB space left. '
		. 'If you wish to expand the available space visit  ' . network_admin_url( 'site-settings.php?id=' . get_current_blog_id() ) . '  and increase the  "' . __( 'Site Upload Space Quota' ) . '."';
	wp_mail( get_site_option( 'admin_email' ), "[ " . wp_specialchars_decode( get_option( 'blogname' ) ) . " ].  Low available space", $message );
    }
}

if ( is_multisite() ) {
    add_action( 'activity_box_end', 'ls_blog_space_mail' );
}