When you create an email, you can save it. Saved emails are saved in the Drafts folder. In addition, emails are automatically saved when you close the new message window, if at least one field has been filled in the new message.
If you haven't made any changes to the email, you can save it as a draft by pressing the Save as draft button at the bottom of the email. After saving, you can close the email using the (Close) button on the Control panel.
To continue working with the email, open it in the Drafts folder and press the (Edit draft) button on the Toolbar in the email viewing window.