How to fix ASP.NET contact form submit issue

See more:

C#

ASP.NET

Javascript

C#4.0

, +

I am trying to send Asp.net Contact form But when clicking on submit button page is refreshing and data are not submitting. the Contact form offline is working fine but after hosting the website it's not submitting data.
if anyone has a solution please send me.
thanks a lot.

What I have tried:

<div class="col-lg-8 text-white">
               Dear visitor is you have any query regarding Our services or Feed Back Please send us.<br>
           </div>
           <div class="col-lg-4">
               <div class="contact-section ">
                   <div class="container">
                       <div class="col-md-form-line">
                           <div class="form-group">
                               <asp:RequiredFieldValidator ID="RequiredFieldValidatorName" runat="server" ErrorMessage="Name is required" ControlToValidate="txtName" Text="*" ForeColor="Red"></asp:RequiredFieldValidator>
                               <asp:TextBox ID="txtName" runat="server" CssClass="form-control" ToolTip="Enter Name" placeholder="Enter Name"></asp:TextBox>
                           </div>
                           <div class="form-group">

                               <asp:RequiredFieldValidator ID="RequiredFieldValidatorEmail" runat="server" ErrorMessage="Email is required" ControlToValidate="txtEmail" Text="*" ForeColor="Red"></asp:RequiredFieldValidator>
                               <asp:RegularExpressionValidator ID="RegularExpressionValidatorEmail" runat="server" ErrorMessage="Please enter a valid email" Text="*" ForeColor="Red" ControlToValidate="txtEmail" ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"></asp:RegularExpressionValidator>
                               <asp:TextBox ID="txtEmail" runat="server" CssClass="form-control" ToolTip="Enter Email" placeholder="Enter Email Id" TextMode="Email"></asp:TextBox>
                           </div>
                           <div class="form-group">

                               <asp:RequiredFieldValidator ID="RequiredFieldValidatorMobileno" runat="server" ErrorMessage="Moble No. is required" ControlToValidate="txtmobileNo" Text="*" ForeColor="Red"></asp:RequiredFieldValidator>
                               <asp:TextBox ID="txtmobileNo" runat="server" CssClass="form-control" ToolTip="Enter Your mobile Number" placeholder="Enter Your mobile Number" TextMode="Phone"></asp:TextBox>
                           </div>

                           <div class="form-group">

                               <asp:RequiredFieldValidator ID="RequiredFieldValidatorsub" runat="server" ErrorMessage="Subject is required" ControlToValidate="txtSubject" Text="*" ForeColor="Red"></asp:RequiredFieldValidator>
                               <asp:TextBox ID="txtSubject" runat="server" CssClass="form-control" ToolTip="Enter Subject" placeholder="Enter Subject"></asp:TextBox>
                           </div>
                           <div class="form-group">

                               <asp:RequiredFieldValidator ID="RequiredFieldValidatorMassage" ControlToValidate="txtMessage" runat="server" ErrorMessage="massage is required" Text="*" ForeColor="Red"></asp:RequiredFieldValidator>
                               <asp:TextBox ID="txtMessage" runat="server" CssClass="form-control" ToolTip="Enter Your Message " placeholder="Start to write Your Message" TextMode="MultiLine" Rows="5"></asp:TextBox>
                           </div>
                           <div>
                               <asp:Button ID="btnsend" runat="server" Text="Send Message" CssClass="btn btn-outline-info" OnClick="btnsend_Click" PostBackUrl="~/Thankyou.aspx"/>
                               <asp:Label ID="Status" runat="server" Text=""></asp:Label>
                               <asp:ValidationSummary HeaderText="Please fix the following error" ForeColor="Red" ID="ValidationSummary1" runat="server" BorderWidth="1" BorderColor="Red" />
                           </div>
                       </div>
                   </div>
               </div>
           </div>