LinkResource

public bool SendEmailToSingle(string toEmail, string Subject, string FormatId)
        {
            try
            {
                var message = new MimeMessage();
                message.To.Add(new MailboxAddress(toEmail));
                message.From.Add(new MailboxAddress(EmailDisplayName, EmailUserName));
                message.Subject = Subject;

                // 获取邮件模板
                string FullFormatPath = Path.Combine(Environment.CurrentDirectory, "Content", FormatId);
                string[] ImgPaths = Directory.GetFiles(Path.Combine(FullFormatPath, "Resources"));

                string HtmlFormat = string.Empty;

                var builder = new BodyBuilder();

                using (FileStream fs = new FileStream(Path.Combine(FullFormatPath, "format.htm"), FileMode.Open))
                {
                    using (StreamReader sr = new StreamReader(fs, Encoding.GetEncoding("gbk")))
                    {
                        HtmlFormat = sr.ReadToEnd();
                    }
                }

                // 将图片加入内嵌资源，并更换邮件中的图片的链接
                foreach (string imgpath in ImgPaths)
                {
                    var image = builder.LinkedResources.Add(imgpath);
                    image.ContentId = MimeUtils.GenerateMessageId();
                    HtmlFormat = HtmlFormat.Replace(Path.GetFileName(imgpath), string.Format("cid:{0}", image.ContentId));
                }

                builder.HtmlBody = HtmlFormat;

                message.Body = builder.ToMessageBody();

                //return message;
                using (SmtpClient client = new SmtpClient())
                {
                    client.ServerCertificateValidationCallback = (s, c, h, e) => true;
                    client.Connect(EmailServerAddress, EmailServerPort, false);
                    client.Authenticate(EmailUserName, EmailPassword);
                    client.Send(message);
                    client.Disconnect(true);
                }

                return true;
            }
            catch (Exception)
            {
                return false;
            }
        }