How to disable an email link after first click

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C#

ASP.NET4

Hi,
I am sending a link in the email with query string to reset password. When user click on link this redirect to user on my website resetPwd.aspx and he/she can reset password successfully in database.
Again if the user is trying to open the link in email, its compulsory that it cant allow the user to open that link. How to block
the email link in the second click?


My C# code

private void sendEmail(string emailTo, string userId)
{
    string UserName = LoginUser.UserName;
    using (StreamReader reader = File.OpenText(Server.MapPath("~/App_Data/ResetPwdEmailBody.txt")))
    {
        string urlBase = Request.Url.GetLeftPart(UriPartial.Authority) + Request.ApplicationPath;
        string verifyUrl = "/Account/UnlockAccount.aspx?uName=" + UserName + "&id=" + userId;
        string fullUrl = urlBase + verifyUrl;
        MailMessage msg = new MailMessage();
        msg.Subject = "Unlock your account";
        msg.IsBodyHtml = true;
        msg.To.Add(new MailAddress(emailTo, UserName));
        msg.Body = reader.ReadToEnd();
        msg.Body = msg.Body.Replace("<%resetPassword%>", fullUrl);
        msg.Body = msg.Body.Replace("<% UserName %>", UserName);
        msg.Priority = MailPriority.High;
        SmtpClient myClient = new SmtpClient();
        myClient.EnableSsl = false;
        try
        {
            myClient.Send(msg);
        }
        catch (Exception ex)
        {
            LoginUser.FailureText = "Email cannot be send. Error: " + ex.Message;
        }
    }

}

Thanks in advance,

Ashok Luhach