afetr click on asp button the page is loading but the event is not raise

<form id="contact-form"<%-- action="http://inthe7heaven.com/homeshop-html/php/contact.php"--%>>

    <label>Name(required)</label>
    <%--<input name="contact-name" type="text">--%>
    <asp:TextBox ID="txtname" runat="server"></asp:TextBox>
    <label>Email(required)</label>
    <%--<input name="contact-email" type="text">--%>
    <asp:TextBox ID="txtemail" runat="server"></asp:TextBox>
    <label>Subject</label>
    <%--<input name="contact-subject" type="text">--%>
    <asp:TextBox ID="txtsubject" runat="server"></asp:TextBox>
    <label>Message</label>
    <%--<textarea name="contact-message"></textarea>--%>
    <asp:TextBox ID="txtmessage" runat="server"></asp:TextBox>
    <%--<input class="big" type="submit" value="Send Message">--%>
    <asp:Button ID="btnsubmit" runat="server" Text="SUBMIT"
        CausesValidation="false" onclick="btnsubmit_Click1" />
   <%-- <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>--%>

</form>

protected void btnsubmit_Click1(object sender, EventArgs e)
{
    MailMessage message = new MailMessage();
    message.From = new MailAddress("EmailRemoved@gmail.com");
    message.To.Add(new MailAddress(txtemail.Text.ToString()));
    message.Subject = txtsubject.Text;
    message.IsBodyHtml = true;
    message.Body = txtmessage.Text.Trim();

    SmtpClient smtp = new SmtpClient();
    smtp.Host = "smtp.gmail.com";
    smtp.EnableSsl = true;
    NetworkCredential NetworkCred = new NetworkCredential("EmailRemoved@gmail.com", "PasswordRemoved");
    smtp.UseDefaultCredentials = true;
    smtp.Credentials = NetworkCred;
    smtp.Port = 587;
    smtp.Send(message);
    ClientScript.RegisterStartupScript(GetType(), "alert", "alert('Email sent.');", true);
}