备注的很清楚，直接使用即可，需要发件邮箱打开SMTP协议

cs文件需要引用using System.Net.Mail;类库

    /// <summary>
    /// 使用SMTP协议发送邮件需要发件用户的邮箱开启SMTP协议
    /// </summary>
    /// <param name="smtpserver">smtp服务器地址</param>
    /// <param name="userName">邮件用户名</param>
    /// <param name="pwd">密码</param>
    /// <param name="nickName">发件人位置显示的昵称</param>
    /// <param name="strfrom">发件人邮箱地址</param>
    /// <param name="strto">收件人向地址</param>
    /// <param name="subj">邮件标题</param>
    /// <param name="bodys">邮件内容</param>
    public static void SendMail(string smtpserver, string userName, string pwd, string nickName, string strfrom, string strto, string subj, string bodys)
    {
        SmtpClient smtpClient = new SmtpClient();
        smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;//指定电子邮件发送方式
        smtpClient.Host = smtpserver;//指定SMTP服务器
        smtpClient.Credentials = new System.Net.NetworkCredential(userName, pwd);//用户名和密码

        //MailMessage _mailMessage = new MailMessage(strfrom, strto);
        MailAddress from = new MailAddress(strfrom, nickName);
        MailAddress to = new MailAddress(strto);
        MailMessage mailMessage = new MailMessage(from, to);
        mailMessage.Subject = subj;//主题
        mailMessage.Body = bodys;//内容
        mailMessage.BodyEncoding = System.Text.Encoding.Default;//正文编码
        mailMessage.IsBodyHtml = true;//设置为HTML格式
        mailMessage.Priority = MailPriority.Normal;//优先级
        smtpClient.Send(mailMessage);
    }