Use reflector to look into OnLoad
implementation of SelectStandardMessage Action Dialog (Sitecore.Modules.EmailCampaign.UI.Dialogs.ActionDialogs, SelectStandardMessage, Sitecore.EmailCampaign
).
I am not sure what code is inside your version(could differs from one revision to another). Mine is only for example:
protected override void OnLoad(System.EventArgs e)
{
if (!Context.ClientPage.IsEvent)
{
this.MessageTree.RootItems = (
from managerRoot in Factory.Instance.GetManagerRoots()
select managerRoot.InnerItem.ID.ToString()).ToList<string>();
this.MessageTree.ExcludeTemplatesForProcess.AddRange(new string[]
{
"{EFC3A4B6-6C05-45F4-8220-2D0291359DD5}",
"{FE8D604D-26F6-426D-A3E2-E4EDFF091B47}"
});
this.MessageTree.ItemFilterForProcess = new System.Func<Item, bool>(SelectStandardMessage.CheckMessageType);
this.MessageTree.ExcludeTemplatesForDisplay.AddRange(new string[]
{
"{D8AD4B81-9269-4868-949F-37D1C28687E5}",
"{69474581-3668-4FED-B0F0-0B88C2532CAE}",
TemplateIDs.Folder.ToString()
});
this.MessageTree.IncludeTemplatesForSelection.Add("{A0EA9681-5C86-43AB-80F7-C522DADF6F12}");
this.MessageTree.StopTemplates.Add("{A0EA9681-5C86-43AB-80F7-C522DADF6F12}");
this.MessageTree.InitTree();
string text = this.IsAutomationRequest ? base.GetParameterValueByKey("StandardMessageId", null) : WebUtil.GetQueryString("selItem");
if (!string.IsNullOrEmpty(text))
{
this.SetSelectedMessageNode(text);
}
}
base.OnLoad(e);
}
When you will review OnLoad
implementation you will get answer what templates are included, what templates are excluded.