I am using the Microsoft.Office.Interop.Outlook.Application to generate an email and display it on the screen before the user can send it. The application is a
For anyone looking for an answer after all those years.
In Outlook 2016 mailItem.HTMLBody already contains your default signature/footer.
In my case I replied to someone. If you want to add a message before just do as shown below. Simple.
MailItem itemObj = item as MailItem; //itemObj is the email I am replying to
var itemReply = itemObj.Reply();
itemReply.HTMLBody = "Your message" + itemReply.HTMLBody; //here happens the magic, your footer is already there in HTMLBody by default, just don't you delete it :)
itemReply.Send();