There are a lot of ways to forward traffic from one domain/website to another. The so-called URL redirection is commonly recommended. In contrast to parking a domain name, a URL redirection can be done only if the domain in question is hosted. What this means essentially is that you can still open any content in case you have a direct link to it and you may create email addresses or subdomains and use them. This kind of feature has numerous practical uses - if you decide to switch your domain address, you may forward the site visitors, but the e-mails with the old one will still be active in case you are making contact with clients or partners. When you have 2 very similar websites and you would like to rebuild one of them, you could redirect the traffic to the other website so that you can avoid losing potential clients, while you'll still be able to access the administration area for the first website and work on it.