Since I upgraded to Yosemite, the Mail app has started asking for passwords for accounts that I no longer use. I didn’t add them when I first set up Yosemite. What’s going on?
iCloud Keychain is what’s going on. At one time you added these accounts to another device you own. When you enabled iCloud Keychain on that device, it made note of these accounts. When you then set up Yosemite and enabled iCloud Keychain on your Mac, iCloud – thinking it was doing you a favour – added those old accounts.
Regrettably there’s no way to edit out this kind of thing in iCloud Keychain – where you can dictate “Sync this one, but not that one.” But hope isn’t entirely lost.
As I recently suggested, you can often put iCloud Keychain to rights by switching it off on every device associated with it, locating the device that has just the information you want synced, configuring iCloud on that device, enabling iCloud Keychain on that device, and then enabling it on your other devices. iCloud should update all your devices with the information from the ‘master’ device.
But email accounts are trickier because sometimes we want one collection of accounts on Device A and a different collection on Device B. (When Device A is your personal Mac and Device B is your Mac at work, for example.) The Internet Accounts system preference provides a way to deal with this.
Open it up, select an account that you don’t want to use on your Mac, and click the minus (–) button at the bottom of the accounts pane. A sheet will appear that offers three options – Remove From All, Cancel and Turn Off Account. Click Turn Off Account and you should see no evidence of this account in the future. If, for one reason or another, that doesn’t work, you can simply disable any options the account has – switch off Mail, Contacts and Calendars, for instance.