Hey Donaldo, the first thing I see in your rewrite rule is that you are redirecting to HTTP, instead of HTTPS. If you want to enforce SSL, you should make sure to have the correct protocol in your redirect.
My regex skills are rusty, but you may want to test your pattern with a hardcoded pattern match like "domainname.com" to make sure it isn't the regex format. If it works without the regex, then at least you will have identified that the problem is with the pattern.
You may want to have "appendQueryString=true" on your action as well, in case you have any forms or campaign codes, etc. that would have "?something=somethingelse" in the URL. You usually want to preserve those on the redirect.
One final note, remember that browsers will cache permanent redirects. While you are testing, you might want to make this a temporary redirect until you get it working, then switch to permanent. Otherwise, you will need to clear the browser cache of redirects to test any changes you make.