There is a really quick easy way that hasn’t been mentioned. See modified below:
public static void GenerateEmail(string emailTo, string ccTo, string subject, string body)
{
var objOutlook = new Application();
var mailItem = (MailItem)(objOutlook.CreateItem(OlItemType.olMailItem));
mailItem.To = emailTo;
mailItem.CC = ccTo;
mailItem.Subject = subject;
mailItem.Display(mailItem);
mailItem.HTMLBody = body + mailItem.HTMLBody;
}
By editing the HTMLBody after you display the mailitem you allow for Outlook to do the work of adding the default signature and then essentially copy, edit, and append.