C# contact form code only works offline?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Net.Mail;
using System.Text;

public partial class contact_us : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnSend_Click(object sender, EventArgs e)
    {
        try
        {
            MailMessage EmailMsg = new MailMessage();
            EmailMsg.From = new MailAddress("noreply@somwhere.com", " Contact Us");
            EmailMsg.To.Add(new MailAddress("EMAIL ADDRESS", "Contact Us"));
            EmailMsg.Subject = "Contact Us Page Message";
            EmailMsg.Body = "Name: " + txtName.Text + "<br />Email: " + txtEmail.Text + "<br />Comments: " + txtComments.Text;
            EmailMsg.IsBodyHtml = true;
            EmailMsg.Priority = MailPriority.Normal;
            SmtpClient MailClient = new SmtpClient("smtp.1and1.com");
            System.Net.NetworkCredential NetworkCred = new System.Net.NetworkCredential();
            NetworkCred.UserName = "noreply@somewhere.com";
            NetworkCred.Password = "PASSWORD";
            MailClient.Port = 587;
            MailClient.Send(EmailMsg);

            lblMessage.Text = "Thank you! Your message has been sent successfully. We will respond as soon as possible to your enquiry.";

            txtName.Text = "";
            txtEmail.Text = "";
            txtEmailConfirm.Text = "";
            txtComments.Text = "";
        }
        catch
        {
            lblMessage.Text = "Sorry! Your message did NOT send. Please check all form field elements and try again.";
            
        }
    }
    protected void btnClrFrm_Click(object sender, EventArgs e)
    {
        txtName.Text = "";
        txtEmail.Text = "";
        txtEmailConfirm.Text = "";
        txtComments.Text = "";
        lblMessage.Text = "";
    }
}


Code block in web.config:

    <system.net>
        <mailSettings>
            <smtp from="noreply@somewhere.com">
                <network host="smtp.1and1.com" password="PASSWORD" userName="noreply@somewhere.com" port="587"/>
            </smtp>
        </mailSettings>
    </system.net>

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