Adding the Email button to the case page layout

Add the Email button to the case page layout so you can reply per email when viewing a case.

1. From Setup, select Object Manager > Case > Case Page Layouts.
2. In the list, click the layout you are using, e.g. Case Layout.
3. In the Case Layout section, click Mobile & Lightning Actions.
4. Drag and drop the Email button to the Salesforce Mobile and Lightning Experience Actions section.

   

5. Click Save.
6. From Setup, select Email > Deliverability. And set Access to Send Email (All Email Services) to All email.