Apple has sent email to iCloud users who have existing me.com and mac.com email addresses, with the news that those of us with the old-style addresses can now receive email to the same user name at icloud.com as well — apart from the domain name, there is no difference in how mail will be treated or received. The icloud.com address is available to use immediately, and merely needs to be added appropriately if you want to have it as your default Reply-to address:
In Apple Mail in Mac OS X (10.7 Lion or 10.8 Mountain Lion), you can select your icloud.com address in the Accounts pane of the Mail Preferences window, but that may not cause it to be used for all replies. Instead, go to the Composing pane, and select it from the Send New Messages pop-up menu. Of course, if you wish to send replies from multiple accounts, the Account of Selected Mailbox option might be better, though even that isn’t entirely predictable (see Joe Kissell’s “Mountain Lion Mail Perturbs Sending Behavior,” 7 August 2012).
In iOS 6, go to Settings > iCloud > Account (your Apple ID) > Advanced:Mail, and under iCloud Account Information, tap Email and then select your new icloud.com address.
In iCloud on the Web, go to the Mail app, click the gear icon in the upper right, and choose Preferences. In the Composing pane, choose your icloud.com address from the Set A Default Address pop-up menu.
Apple says that if you had a working mac.com email address as of 9 July 2008, kept your MobileMe account active, and moved to iCloud before 1 August 2012, you can use mac.com, me.com or icloud.com. If you created an iCloud account before 19 September 2012 or moved an active MobileMe account to iCloud before 1 August 2012, you can use either me.com or icloud.com (but not mac.com). And if you created an iCloud account on or after 19 September 2012, you’re stuck with only icloud.com. I can see why Apple would deprecate the me.com domain after the demise of MobileMe, but it’s a little surprising that they aren’t letting new users use the mac.com domain, which would seem to be promoting Apple computers with every message.