By default, autosaving of emails and templates is enabled in Organization settings menu, you can disable it as displayed below if you want.
In addition, you have an option to save emails manually inside the editor at any time.
When autosaving is disabled and you try to exit without saving, you will see the following warning window which reminds you of the possible loss of unsaved changes and helps to save them.
While saving is in process, you will see the following indicators. When they disappear, it means email is saved successfully.
Please note that a stable internet connection is required to save changes correctly.
In addition, you can use Save email and exit option to save your work as a new email.