Originally Posted by joejoejoejeo
I don't want to use alias because it's bad for SEO and i don't want to use redirect 301 and other kind of redirections because i want really that the user access the website through both domains transparently and take no SEO risk.
Sorry, but that's impossible. It's called duplicate content. Using Domain Alias is the proper way to achieve what you want to do. From there, I would recommend using .htaccess and mod_rewrite to control your traffic and url structures. I use this exact system.
If you truly want two domains to point to, and serve, the exact same webroot, then you are creating a domain alias, no matter what means you use to achieve it.
On a side note, using 301 redirection avoids the duplicate content penalty which is why it is the preferred method for SEO.