How do I fix System.Net.Mail.SmtException: 'Cannot get IIS pickup directory' error?

I am trying to send email using the EmailButton_Click code. However I am getting the error on this line smtp.Send(mailMessage)

The error is System.Net.Mail.SmtpException: 'Cannot get IIS pickup directory.'

Can someone help me fix it please?

protectedvoid EmailButton_Click(object sender, EventArgs e)
{//get selected email
    EmailButton.Visible = true;string requestor = RequestorDropDownList.SelectedValue.ToString();string message = "The following records have been prepped for processing.  Valid cases will be processed.";if (requestor.Length >0)
         message = string.Format(message);using (MailMessage mailMessage = new MailMessage())
        {
            mailMessage.From = new MailAddress("NoReply_FTA@courts.state.mn.us");//Uncomment after testing in Deve June 2019 
            MailAddress to = new MailAddress(requestor);
            mailMessage.To.Add(to);string ccEmailAddress = "okaymy1112@mail.com";if (ccEmailAddress.Length >0)
            {
                MailAddress ccto = new MailAddress(ccEmailAddress);
                mailMessage.CC.Add(ccto);
            }
                mailMessage.Subject = "FTA Case Reset Notice";
                mailMessage.Body = message;
                SmtpClient smtp = new SmtpClient();
                smtp.DeliveryMethod = SmtpDeliveryMethod.PickupDirectoryFromIis;
                smtp.Send(mailMessage);//Error on this line
        }string msg = "No batches were found";
            Response.Write("<script>alert('" + msg + "')</script>");
}