网易，新浪，谷歌，腾讯的邮件服务都支持stmp协议。

using System.Net.Mail;

　　　　 MailMessage message = null;        SmtpClient client = null;        public void Send()        {            try            {                string argFrom = "test@gmail.com";                string argTo = "test@hotmail.com";                string argSubject = "邮件测试";                string argBody = "test";                message = new MailMessage(argFrom, argTo, argSubject, argBody);                message.BodyEncoding = System.Text.Encoding.UTF8;                message.IsBodyHtml = true;                message.Attachments.Add(new Attachment(@"D:\2e2sd42lxj.jpg"));                client = new SmtpClient("smtp.gmail.com");                client.UseDefaultCredentials = false;                //client.Port = 465; // foxmail需要使用此端口，未验证                // client.Port =587；// gmail需要使用此端口，本人用普通邮箱测试，使用此端口反而提示：由于连接方在一段时间后没有正确答复或连接                client.EnableSsl = true; // gmail需要此安全设置,qq则不需要                client.Credentials = new System.Net.NetworkCredential("test@gmail.com", "password");                client.DeliveryMethod = SmtpDeliveryMethod.Network;                client.Timeout = 100000;                client.Send(message);            }            catch (Exception ex)            {                Console.WriteLine(ex.Message);            }        }