Manually configuring an iCloud email account | Macworld: Some people have had some difficulty making older MobileMe accounts work with iCloud. And yet when they try to manually set up such an account, they’re thwarted because there doesn’t appear to be a way to fiddle with iCloud’s IMAP and SMTP settings. But you can if you know the secret.
And here’s that secret. While in Mail’s Accounts setting, click on the Plus button and enter your iCloud address and password as you normally would. The button at the bottom will read Create. Hold down the Option key and that button changes to read Continue. Click on Continue. Instead of your account being set up for you, you can now set it up manually.