On my wife's MacBook Air, using Mavericks, I want to set up her Mac Mail to use her iCloud account BUT to have it set so when I reply to an e-mail, or create an e-mail from scratch for that matter, send from a custom domain e-mail address that she has. The custom domain is not an @icloud.com address. Setting up iCloud as-is is very easy. But I can't seem to figure this alteration out. Thanks!