I've just installed 10.10 on my spare machine (clean install) and logged into my iCloud account. It automatically set up a third-party (ie. non-iCloud) email account that I use on my 10.9 desktop. I don't want those emails coming into that machine, so I went into Sys Prefs > Internet Accounts and removed the account. Lo and behold, it went and removed the account from my 10.9 machine too! When I re-added it on 10.9 (thankfully an IMAP account so nothing was actually deleted), it then reappeared on 10.10. It seems that iCloud Keychain is doing this, as turning off Keychain on the 10.10 machine has stopped it from copying account settings around. However, I have of course lost the ability to use Keychain. I suspect that if I turn it back on then it'll start copying settings all over the place again. How can I get around this? I still want to be able to use iCloud Keychain so that I can log into websites easily, but I don't want to get work emails on my "relaxation" machine. Help!