Greetings.
I need to change my Apple ID to a new email address (currently @ml1.net) to a different domain, @fastmail.fm
I've already gone to Apple.com to login to my account and changed my email address wherever I could there, but it doesn't actually change the email address associated with my Apple ID. For example, my Mac asks me for the password associated with my @ml1.net which does not work because I changed my email address to @fastmail.fm but it still holds my Apple ID to the @ml1.net email address. I tried going into the iCloud System Preferences in OS X, but there is no field there for me to change my email address associated with my Apple ID that Apple keeps asking me for. I tried resetting my password and entering my new email address and just chose to answer security questions, but that didn't work, and I'm forced to set a new password rather than use the one that I had. But even weirder, once this is done, sometimes I am asked for the password for @ml1.net , while other times I am asked for the password for @fastmail.fm , which is what I want (for example, to sign in to view purchased items in App Store).

Also, I tried going to
https://www.apple.com/support/country/
and clicking United States at the bottom right, but I received the following error message:

"Safari Can't Open the Page
Too many redirects occurred trying to open "https://support.apple.com/index.html". This might occur if you open a page that is redirected to open another page which then is redirected to open the original page."

How do I change the email address associated with my Apple ID to my @fastmail.fm email once and for all among all of my devices?

[Waragainstsleep]

If you can sign in ok on the Apple website(s), then for some services like the iCloud system pref pane on your Mac, and the setting on your phone/iPad you might have to sign out and sign back in in order to change it. I would take a backup of your contacts somewhere before doing that on iOS just in case.

Apple tends to leave old addresses active or semi active because for example iTunes purchases with DRM will probably always ask for the original email address as they have been tagged with it.
I can still log into iCloud with my .mac or .me addresses last I tried.

Wish I had known that before choosing a new password. Signing out (which required System Preferences required that it back up my data for me) and signing back in worked.

[...deleted...]