下面用到的邮件账号和密码都不是真实的，需要测试就换成自己的邮件账号。需要引用：
using System.Net.Mail;
using System.Text;
using System.Net;程序代码：MailMessage myMail = new MailMessage(); //创建邮件实例对象myMail.From = new MailAddress(""); //发送者，要和邮件服务器的验证信息对应，不能随便更改myMail.To.Add(new MailAddress("")); //接收者myMail.Subject = "C#发送Email"; //邮件标题myMail.SubjectEncoding = Encoding.UTF8; //标题编码myMail.Body = "this is a test email!"; //邮件内容myMail.BodyEncoding = Encoding.UTF8; //邮件内容编码myMail.IsBodyHtml = true;     //邮件内容是否支持htmlSmtpClient smtp = new SmtpClient(); //创建smtp实例对象smtp.Host = "mail.sina.com"; //邮件服务器SMTPsmtp.Port = 25;                  //邮件服务器端口smtp.Credentials = new NetworkCredential("", "123456"); //邮件服务器验证信息smtp.Send(myMail); //发送邮件使用Gmail邮箱发送邮件示例MailMessage myMail = new MailMessage();myMail.From = new MailAddress("");myMail.To.Add(new MailAddress(""));myMail.Subject = "C#发送Email";myMail.SubjectEncoding = Encoding.UTF8;myMail.Body = "this is a test email from gmail!<a href='http://www.sina.com.cn'>sina</a>";myMail.BodyEncoding = Encoding.UTF8;myMail.IsBodyHtml = true;SmtpClient smtp = new SmtpClient();smtp.Host = "smtp.gmail.com";smtp.Port = 587; //Gmail的smtp端口smtp.Credentials = new NetworkCredential("", "123456");smtp.EnableSsl = true; //Gmail要求SSL连接smtp.DeliveryMethod = SmtpDeliveryMethod.Network; //Gmail的发送方式是通过网络的方式，需要指定smtp.Send(myMail);使用QQ邮箱发送邮件示例MailMessage myMail = new MailMessage();myMail.From = new MailAddress("");myMail.To.Add(new MailAddress(""));myMail.Subject = "C#发送Email";myMail.SubjectEncoding = Encoding.UTF8;myMail.Body = "this is a test email from QQ!";myMail.BodyEncoding = Encoding.UTF8;myMail.IsBodyHtml = true;SmtpClient smtp = new SmtpClient();smtp.Host = "smtp.qq.com";smtp.Credentials = new NetworkCredential("", "123456");smtp.Send(myMail);