It looks to me that you must be using a single site environment.
If you configure your nginx with virtual hosts put your domain in the correct virtual so that:-
1. your site is shown when you use your domain to resolve to your IP
2. Any other domain resolving to the same IP get another site with a standard index.html page
In that page place, inside the <head> and </head>
<meta http-equiv="refresh" content="0;URL='http://www.quackquack.in'" />
This does not require .htaccess rules.
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