iCloud account linked to a .mac email address
My iCloud account is linked to my old .mac email address which I haven't used in forever and assume is no longer functional. In the mail app settings I see the iCloud account it is inactive and attempting to enable it yields no results.
From my research I understand that .mac emails are no longer available and I need to use the more recent iCloud domain however when I go to set up an @icloud.com email my @mac.com name isn't available as an option. I was able to grab FirstnameLastname@mac.com and would like to continue using FirstnameLastname@icloud.com for my Apple ID.
Am I correct in thinking another user has already claimed the iCloud version of my email or is it possible that I can gain access to the @iCloud account that matches my @mac account?