เพิ่มลายน้ำข้อความไปยัง EML ผ่าน C #

mail.Attachments.Add("watermark", imageBytes);

var html = mail.BodyHtml;
var htmlDocument = new Aspose.Html.HTMLDocument(mail.BodyHtml, "");

var attachment = mail.Attachments.Find(x => x.LongFileName == "watermark");
attachment.SetContentId("watermark");

var bodyHtml = htmlDocument.Body.InnerHTML;

var watermarkHtml = $@"watermarkHtml";

htmlDocument.Body.InnerHTML = watermarkHtml;

var folderPath = Path.Combine(Config.Configuration.OutputDirectory, Guid.NewGuid().ToString());
var filePath = Path.Combine(folderPath, "Merged.html");

htmlDocument.Save(filePath);

var content = System.IO.File.ReadAllText(filePath);

Directory.Delete(folderPath, true);

mail.SetBodyContent(content, BodyContentType.Html);