For the base URL, you do not need a RewriteCond , just a RewriteRule :
RewriteRule forum http://83answers.com [R,L]
For the query string, you were almost there:
RewriteCond %{QUERY_STRING} forum RewriteRule .? http://83answers.com [R,L]
Combined Rules:
RewriteRule forum http://83answers.com [R,L] RewriteCond %{QUERY_STRING} forum RewriteRule .? http://83answers.com [R,L]
Please note that you must enable http:// . If you just use 83answers.com , the server is trying to redirect the URL of your server. For example, it redirects http://test.guru99.com/forum/xyxyxzz to http://test.guru99.com/83answers.com , which is not suitable.
Ed cottrell
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