private static string Host = System.Configuration.ConfigurationManager.AppSettings["SMTPURL"].ToString(); //SMTP服務器地址
private static string Account = System.Configuration.ConfigurationManager.AppSettings["SMTPACCOUNT"].ToString(); //SMTP服務帳號
private static string Pwd = System.Configuration.ConfigurationManager.AppSettings["SMTPPWD"].ToString(); //SMTP服務密碼
private static string From = System.Configuration.ConfigurationManager.AppSettings["SMTPFROM"].ToString(); //發送方郵件地址

        public static int SendMail(string subject, string body, string toMail,ref string msg,string icon="")
        {
            int reslult = -1;
            string To = System.Web.HttpUtility.UrlDecode(toMail.Trim());   // 收件方郵件地址

            SmtpClient _smtpClient = new SmtpClient();
            _smtpClient.DeliveryMethod 
 
= SmtpDeliveryMethod.Network;//指定電子郵件發送方式
            _smtpClient.Host = Host; ;//指定SMTP服務器
            _smtpClient.Credentials = new System.Net.NetworkCredential(Account, Pwd);//用戶名和密碼
            MailMessage _mailMessage = new MailMessage(From, To);

            AlternateView htmlBody = AlternateView.CreateAlternateViewFromString(body, null
 
, "text/html");
            if (!string.IsNullOrEmpty(icon))
            {
                LinkedResource lrImage = new LinkedResource(icon, "image/gif");
                lrImage.ContentId = "weblogo";
                htmlBody.LinkedResources.Add(lrImage);
                _mailMessage.AlternateViews.Add(htmlBody);
            }

            _mailMessage.Subject = System.Web.HttpUtility.UrlDecode(subject); //主題 
            _mailMessage.Body = System.Web.HttpUtility.UrlDecode(body);//內容
            _mailMessage.BodyEncoding = System.Text.Encoding.UTF8;//正文編碼
            _mailMessage.IsBodyHtml = true;//設置為HTML格式
            _mailMessage.Priority = MailPriority.High;//優先級
            try
            {
                _smtpClient.Send(_mailMessage);
                reslult = 1;
                msg = "發送成功";
            }
            catch (Exception ex)
            {
                reslult = -1;
                msg = ex.Message;
            }
            return reslult;
        }

.Net 發送郵件