Represents an abstract Apex class that provides the context for
running the standard Email Action on Case Feed and the container of the Email Message fields
for the action payload. You can override the target fields before the standard Email Action
is rendered.
You cannot extend this abstract class. You can use the getter methods when using it in
the context of QuickAction.QuickActionDefaultsHandler. Salesforce provides a class that
extends this class (See
QuickAction.SendEmailQuickActionDefaults.)