The accepted answer worked great for me. However in order to get the email body (description) to populate from the template on page load, I had to pass an empty string (with a space) as the description parameter. Here is my final solution:
//Set template lookup parameter to pass to email
var template = {
id: {email template id},
name: {email template name},
entityType: “template”
};
//Set regardingobjectid lookup
var regardingLookup = {
id: formContext.data.entity.getId().replace(/[{}]/g, ”),
name: formContext.data.entity.getPrimaryAttributeValue(),
entityType: “incident”
};
var parameters = {
formId: emailFormId,
regardingobjectid: regardingLookup,
templateid: template,
description: ” ” // Here is where I had to add an empty description (must have space character)
};
var entityFormOptions = {};
entityFormOptions[“entityName”] = “email”;
Xrm.Navigation.openForm(entityFormOptions, parameters);
