How to Reinstall the Macintosh Mail Clientby Avery Martin
The Apple Mail client on Mac OS X Mavericks doesn't come with a separate installation package that you can install individually. However, your Mac does have certain healing capabilities that allows you to reinstall the entire operating system without losing files, folders and applications. Running the Mac OS X installer makes it possible to restore any missing native applications, repair corrupt files and get your computer working again.
Reinstall Mail Client
Reinstalling your Mail client requires you to run the Mac OS X installer. Restart your computer and hold down "Command-R" after you see the gray start screen appear. When the recovery utility launches, select your Wi-Fi network and provide a password for the network. You can also connect your computer directly to your router with an Ethernet cable. Choose the option to "Reinstall Mac OS X," select your hard drive and click the "Continue" button. During the process you may need to provide the Apple ID and password that you used to purchase Mac OS X Mavericks.