Como desinstalar o Apple Mail App em um MacBook Pro e reinstalei-o?
How do I uninstall Apple Mail app on a Macbook Pro and then reinstall it?
To uninstall try with AppCleaner, it's free in the AppStore. Apple Mail is a system app so, in AppCleaner, try double click on the checkbox and then proceed to Delete the app.
For Reinstall. Apparently you'll need to do a reinstallation of OSX. According to this Apple page, a reinstallation wont affect your files, can't tell for myself, I've never done that. Simply make a backup before anything and may the force be with you.