Why is my form validation not working when I have my validation summary in place - asp.net-mvc

Question

I have a #HTML.ValidationSummary within my form which is in a modal (dialog), however, it does not seem check if the form inputs have valid values before the modal closes. I will like the validation summary to be displayed, as shown below, my view model has validation attributes on it's properties.
#using (Html.BeginForm("Index", "Home", null, FormMethod.Post, new { Id = "frmSendEmail", #class = "form-horizontal" }))
{
<div class="modal fade" id="modalSendEmail" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
<div class="modal-dialog" role="document">
<div class="modal-content">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">×</span></button>
<h4 class="modal-title" id="modalLabel">Email</h4>
</div>
<div class="modal-body">
#Html.ValidationSummary("Oops! Seems like we are missing some information, please provide details for the required field marked with a *", new { #class = "alert alert-danger" })
<div class="form-group">
<label for="txtName" class="col-sm-2 control-label">* Name:</label>
<div class="col-sm-10">
#Html.TextBoxFor(model => model.SenderName, null, new {id = "txtName", #class = "form-control", placeholder = "Name"})
#Html.ValidationMessageFor(model => model.SenderName)
</div>
</div>
<div class="form-group">
<label for="txtEmail" class="col-sm-2 control-label">* Email:</label>
<div class="col-sm-10">
#Html.TextBoxFor(model => model.SenderEmail, null, new { id = "txtEmail", #class = "form-control", placeholder = "Email", type = "email" })
#Html.ValidationMessageFor(model => model.SenderEmail)
</div>
</div>
<div class="form-group">
<label for="txtTelephone" class="col-sm-2 control-label">Telephone:</label>
<div class="col-sm-10">
#Html.TextBox("telephone", null, new { id = "txtTelephone", #class = "form-control", placeholder = "Telephone" })
</div>
</div>
<div class="form-group">
<label for="txtEnquiry" class="col-sm-2 control-label">* Enquiry:</label>
<div class="col-sm-10">
#Html.TextAreaFor(model => model.SenderEnquiry, new { id = "txtEnquiry", #class = "form-control", rows = "5" })
#Html.ValidationMessageFor(model => model.SenderEnquiry)
</div>
</div>
</div>
<div class="modal-footer">
<button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
<button type="submit" class="btn btn-warning" id="btnSendEmail">Send</button>
</div>
</div>
</div>
</div>
}
**Model**
public class Enquiry
{
[Required]
public string SenderName { get; set; }
[Required]
public string SenderEmail { get; set; }
public string SenderTelephone { get; set; }
[Required]
public string SenderEnquiry { get; set; }
}

Answer 1

In the View, change
#Html.ValidationSummary("Oops! Seems like we are missing some information, please provide details for the required field marked with a *", new { #class = "alert alert-danger" })
to
#Html.ValidationSummary(true, "", new { #class = "alert alert-danger" })
In the controller:
public ActionResult Index(Enquiry emailEnquiry)
{
if (ModelState.IsValid)
{
// all done
return ...
}
ModelState.AddModelError("", "Something is invalid.");
return View(emailEnquiry); // don't forget returning with model
}