Mail Account Preferences freezes when trying to save edited alias
The iCloud account in Mail 10.9 automatically added an email alias I don't wish to use. It can neither be edited, added to or deleted. Any attempt freezes the Preferences pane and the app must be quit to dismiss it, changes unsaved. Live chat with Apple Support was unable to resolve this.
MacBook Pro (Retina, 15-inch, Mid 2014), OS X El Capitan (10.11)