<input type="text" name="Mail" id="Mail"/>
     <span>*请输入邮箱</span><br/>
     <asp:Button ID="zhuce" runat="server" Text="tijiao" OnClick="btn" />

protected void btn(object sender, EventArgs e)
    {
      string mail = Context.Request["Mail"];
      MailMessage message = new MailMessage();
      message.From = new MailAddress("######", "#####");//发件人地址
      message.To.Add(mail);//目标发件地址
      message.Subject = "dssdds";//邮件标题
      message.Body = "nihao";//邮件内容
      //发送邮件的smtp服务器地址
      SmtpClient smtp = new SmtpClient("smtp.163.com");
      smtp.Credentials = new NetworkCredential("#########", "######");//发件人的用户名和密码
      smtp.Send(message);
    }