What will happen to my email address?: "As a current .Mac member, your @mac.com email will continue to work as it always has. But your account will also be given a new email address @me.com.
Even if you do nothing, email sent to either address will still arrive in your inbox and you can send email from either address in MobileMe Mail on the web. However, in order to send email from your me.com address in your email client (e.g. the Mail application on your Mac), you will need to set up your me.com account in Mail preferences.
You may"
.Mac Tips - http://www.mac.com/web/en/Tips/Tips.html