How to send an email notification to the last content Editor who submitted the item for approval when the item got approved/published?

As a user who submitted a content item for approval, I would like to get a notification back if the item was published or rejected.

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One of the approach is to store the LastModifiedBy value of the WaitingApproval item and get the user email from this value and store it in a property (e.g. LastModifierEmail) before it gets Approved and then once the item got approved(e.g. Published) send the email to the email address that was stored in the LastModifierEmail.

Here is a sample code for the workflow of Custom Dynamic Module Items (e.g. Dynamic Module: CustomArticles and Dynamic Type: CustomArticle):
 

public class Global : System.Web.HttpApplication
    {

        protected void Application_Start(object sender, EventArgs e)
        {
            Bootstrapper.Initialized += Bootstrapper_Initialized;
        }
        public static void Bootstrapper_Initialized(object sender, ExecutedEventArgs args)
        {
            if (args.CommandName == "Bootstrapped")
            {
                EventHub.Subscribe<IDynamicContentUpdatingEvent>(evt => IDynamicContentUpdatingEvent(evt));
                EventHub.Subscribe<IDynamicContentUpdatedEvent>(evt => IDynamicContentUpdatedEvent(evt));
            }
        }
        private static void IDynamicContentUpdatingEvent(IDynamicContentUpdatingEvent eventInfo)
        {
            var dynamicModuleManager = DynamicModuleManager.GetManager();
            var userManager = UserManager.GetManager();
            if (eventInfo.Item.GetType().FullName == "Telerik.Sitefinity.DynamicTypes.Model.CustomArticles.CustomArticle" && eventInfo.Item.Status == Telerik.Sitefinity.GenericContent.Model.ContentLifecycleStatus.Temp && eventInfo.Item.ApprovalWorkflowState == "AwaitingApproval")
            {
                var masterItemBeforeApproved = (DynamicContent)dynamicModuleManager.Lifecycle.GetMaster(eventInfo.Item);
                if (masterItemBeforeApproved.LastModifiedBy != Guid.Empty)
                    lastModifierEmail = userManager.GetUser(masterItemBeforeApproved.LastModifiedBy).Email;
            }
        }
        private static void IDynamicContentUpdatedEvent(IDynamicContentUpdatedEvent eventInfo)
        {
            if (eventInfo.Item.GetType().FullName == "Telerik.Sitefinity.DynamicTypes.Model.CustomArticles.CustomArticle" && eventInfo.Item.Status == Telerik.Sitefinity.GenericContent.Model.ContentLifecycleStatus.Master && eventInfo.Item.ApprovalWorkflowState == "Published")
            {
                //Send email to the lastModifierEmail manually here
                var email = lastModifierEmail;
            }
        }
        public static string lastModifierEmail { get; set; }
   }

Note: The is for the Custom Dynamic Module "CustomArticles" with the type "CustomArticle" (e.g. "Telerik.Sitefinity.DynamicTypes.Model.CustomArticles.CustomArticle"), you will need to change the CustomArticles.CustomArticle according to your custom module.

For the built-in dynamic types and the pages, IDataEvent can be used to implement the above functionality.

References to Other Documentation:

Sitefinity Documentation, IDataEvent https://www.progress.com/documentation/sitefinity-cms/for-developers-idataevent

Progress Article(s):

000081847 How to catch the Publish, Unpublish and Save as draft events using API