问如何在发送电子邮件之前向asp.net中的客户端显示电子邮件框

EN

To: <asp:TextBox runat="server id="To_TB /><br />
Subject: <asp:TextBox runat="server" id="Subject_TB" /><br />
Body:<br />
<asp:TextBox runat="server" id="Body_TB" TextMode="Multiline" /
<br />
<asp:Button runat="server" id="Submit_BTN" Text="Send Email" OnClick="Submit_BTN_Click" />

protected void Submit_BTN_Click(object sender, EventArgs e)
{
    MailMessage msg=new MailMessage("myserver@mysite.com", To_TB.Text, Subject_TB.Text, Body_TB.Text);
    SmtpClient client=new SmtpClient("myemailserver@mydomain.com");
    client.Send(msg);
}