I want to deploy exchange server 2013 but i have an issue, i have registerd domain called example.com, and i set my DC as this domain example.com, but now i do not have this domain so i register for a new one with the same name but with diffrent end example.net, now the problem that i want to deploy exchange with the new domain(example.net) so i can use it to send outside my organization now i have to do to use the new domain, shall i have to creat new chield domain or start from scratch or what Thanks in advanced (sorry for my poor english)

The Active Directory domain does not have to be the same as the Exchange domain. When you install Exchange, it will take the AD domain if you don't already have Exchange installed, but you can change that anytime you want.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

ok, now i installed exchange server 2013 and the default domain for any new created email is user@example.com, so from where or how can i change it to be like this user@example.net and use new domain example.net and make it be the default for the organization.

You will change it in Accepted Domains and E-Mail Address Policy.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."