Use Drafts to Perfect Your List Emails
Where: This change applies to Lightning Experience in the Essentials, Professional, Enterprise, Performance, Unlimited, and Developer editions.
How: From a contact or lead home page, click Send List Email and start writing the content. To save your changes, click Save as Draft.
To resume editing the list email, go to the List Email home page.
Find your draft list email (1) and continue editing (2). When you’re done editing, save the draft again or send the list email.