Apple today released a new version of Mail for OS X Yosemite, fixing an issue that could prevent users from composing a message



From MacRumors:

The update is available to all developers with the Yosemite Developer Preview installed, as well as public beta testers. The software can be downloaded through the software update function of the Mac App Store.

  Apple Releases OS X Yosemite Mail Update for Developers and Public Beta Testers