I need help to fix this Mod_Rewrite issue

[mexabet]

I need help to configure this: After my web host installed a mail server, my add-on domain (e.g. addondomaintwo.biz) can now be accessed through http://mail.addondomainone.com/addondomaintwo.biz/.

I tried to fix the issue by adding the following code to the public_html/.htaccess, but it didn't work:

RewriteCond %{HTTP_HOST} ^mail.addondomainone.com$
RewriteRule ^mexabet\.biz\/?$ "http\:\/\/www\.addondomaintwo\.biz\/" [R=301,L]

I simply want http://mail.addondomainone.com/addondomaintwo.biz to redirect to http://www.addondomaintwo.biz/

I'll appreciate your time and help.