get_comment_author_email( int|WP_Comment $comment_ID )

function get_comment_author_email( $comment_ID = 0 ) {
	$comment = get_comment( $comment_ID );

	/**
	 * Filters the comment author's returned email address.
	 *
	 * @since WP-1.5.0
	 * @since WP-4.1.0 The `$comment_ID` and `$comment` parameters were added.
	 *
	 * @param string     $comment_author_email The comment author's email address.
	 * @param int        $comment_ID           The comment ID.
	 * @param WP_Comment $comment              The comment object.
	 */
	return apply_filters( 'get_comment_author_email', $comment->comment_author_email, $comment->comment_ID, $comment );
}