As one of the many people who purchased a MobileMe subscription in years past, you've probably already made the transition to iCloud and haven't looked back. In July of 2012, Apple noted during iOS 6 beta testing that new icloud.com addresses would be created for anyone using Apple's cloud computing solution as well as former MobileMe members. The transition to icloud.com email is apparently complete, as Apple is sending out a note to those MobileMe members telling them about their new email address option.
While Apple created a new icloud.com email address for anyone who had a mac.com or me.com address in the past, any one of those three domain prefixes can be used. An email sent to firstname.lastname@example.org, for example, appears in any email@example.com or firstname.lastname@example.org inbox as well. Here's the text of the Apple email:
All new iCloud Mail accounts now come with an @icloud.com email address. As an existing user, we'd like to offer you this new address as well. We have reserved [MobileMe user name]@icloud.com for you, and you can now use this address with your iOS devices and computers by following these simple instructions.
If you prefer, you can continue to use your current email address just as you always have.
No matter which address you use, you'll continue to receive all your mail, whether it's sent to your @me.com, @mac.com, or @icloud.com address.
For many of us, we'll keep the me.com or mac.com address ... but thanks for asking, Apple.