Q: I did all that this article asked, and my @mac.com account does not work for some reason now. How can I fix this?

I have the same issue. I just 'tested' my @mac.com email address, but it bounces back.

I read all this (here):

• If you created an iCloud account on or after September 19th, 2012, your email address and aliases will end with @icloud.com. Learn more about @icloud.com email addresses.
• If you created an iCloud account before September 19th, 2012 or moved to iCloud with an active MobileMe account before August 1st, 2012, you will have both @me.com and @icloud.com email addresses.
• If you had a working @mac.com email address as of July 9th, 2008, kept your MobileMe account active, and moved to iCloud before August 1st, 2012, you will be able to use @icloud.com, @me.com, and @mac.com email addresses with your iCloud account.

and the last bullet applies to me. I am/was a .mac client before 2008, then MobileMe and now iCloud - but my 2mac.address is not working any more. I have to admit I did not use it in a while, but I have old emails that proof that it obviously still worked until at least late 2011.

Also cannot tell if it stopped working after I signed up for iCloud.