Add a 301 redirect that covers an entire domain
Options +FollowSymLinks
RewriteEngine on
RewriteCond %{HTTP_HOST} ^www.domain1.com$
RewriteRule ^(.*)$ http://www.domain2.com/$1 [R=301,L]

Add a 301 redirect that covers an entire domain
Options +FollowSymLinks
RewriteEngine on
RewriteCond %{HTTP_HOST} ^www.domain1.com$
RewriteRule ^(.*)$ http://www.domain2.com/$1 [R=301,L]