Solution2:
This following code takes care of permalinks in WorPress and it is recommended to keep the beginning and ending WordPress lines so that WordPress is able to locate it and modify it as needed. You may already have all this and are just not displaying it. I do not know.
# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# END WordPress
In the other section you probably need to remove the trailing / after folder2 like so:
RewriteEngine On
RewriteCond %{REQUEST_URI} ^/folder
RewriteRule ^(.*)$ http://www.domainB.com/folder1/folder2 [P]