Brent Simmonds is a Mac developer and there's been a discussion about the Mac email client landscape brewing for a while.  The Coccoa requirement is due to the unstated context that we're talking about an email client for Mac OS X.<p>By shipping Mail with every Mac, Apple basically makes it impossible for someone else to come along and compete with a commercial product.  Thunderbird, while a fantastic piece of work, doesn't behave quite like a Mac-native application.  By saying it's got to be Coccoa, Brent's saying it has to be through-and-though Mac-like.