Check out this: https://forum.mendix.com/link/questions/3322
The snapshot of the data does not transfer data from your local environment to the cloud.
What Maarten said.
You can use this Appstore module: https://appstore.home.mendix.com/link/app/2743/ to easily import and export e-mail templates. This way you don’t have to (try to) recreate them on every environment.