This Redirect htaccess code below in an htaccess file in the old site’s folder would redirect all old site pages and posts to identical matching pages and posts with the same identical structure on the new site/domain.
RedirectMatch 301 ^/$ http://www.newdomain.com/$1
For some web hosts you need to include the folder name where the website is physically installed. olddomain.com would be the name of the folder and not the URL|URI name.
RedirectMatch 301 ^/olddomain.com$ http://www.newdomain.com/$1
See this forum topic for recommendations when migrating/moving/cloning websites: http://forum.ait-pro.com/forums/topic/migrating-moving-or-cloning-websites/#post-20407