Fail to add multiple attachments to mail message in net core web app

Hi,

I try to construct and send an email message in a web net core app. The message need to have maximal 3 attachments, provided by the user who navigates the site. First is mandatory, and at least one from the two remaining attachments is also mandatory.

If I attach only one (e.g. first) attachment, all is ok. But when I attach at least 2 attachments, I have an error.

The relevant portions of code are bellow (the model, the view, and the controller). At the very bottom is the error:

/*Relevant part of model*/

public class Inscrieri.Inima.Models
{
//
        public IFormFile CopieCN { get; set; }
        public IFormFile CopieCIT { get; set; }
        public IFormFile CopieCIM { get; set; }
//
}


/*Relevant part of view*/

<div class="separator"></div><div><strong>Certificat de Nastere Copil</strong><p> (in format *.jpg sau *.png):</p></div><div>
                @Html.TextBoxFor(model => model.CopieCN, new { type = "file" })</div><div><strong>Act de Identitate Tata:</strong><p> (in format *.jpg sau *.png):</p></div><div>
                @Html.TextBoxFor(model => model.CopieCIT, new { type = "file" })</div><div><strong>Act de Identitate Mama:</strong><p> (in format *.jpg sau *.png):</p></div><div>
                @Html.TextBoxFor(model => model.CopieCIM, new { type = "file" })</div><div class="separator"></div><div class="clearfix"></div><div><input type="submit" value="Trimite" /></div><div class="separator"></div><span style="color:green">@ViewBag.Message</span>


/*Relevant part of controller*/

        [HttpPost]
        public IActionResult Index(EmailModel model)
        {
            using (MailMessage mm = new MailMessage("sender.email@gmail.com", "first.recipient@email.com, second.recipient@email.com"))
            {
                mm.Subject = "Cerere de inscriere pentru: " + model.Prenume + " " + model.Nume;
                mm.Body = "Va rog sa aprobati inscrierea copilului " + model.Prenume + " " + model.Nume + " nascut(a) la data de " + model.DataNasterii + ", avandu-i ca parinti pe " + model.NumeTata + " si " + model.NumeMama + " in grupa: " + model.Grupa+". "+ Environment.NewLine + "Locul de munca al parintilor: " + model.LocDeMunca;
                mm.IsBodyHtml = true;
                mm.Priority = MailPriority.High;


                //atasam CN copil
                if (model.CopieCN.Length > 0)
                {
                    string fileNameCN = Path.GetFileName(model.CopieCN.FileName);
                    Attachment file1 = new Attachment(model.CopieCN.OpenReadStream(), fileNameCN, MediaTypeNames.Application.Octet);
                    mm.Attachments.Add(file1);
                    //file1.Dispose();
                    //mm.Attachments.Add(new Attachment(model.CopieCN.OpenReadStream(), fileNameCN, MediaTypeNames.Application.Octet));
                }
                //atasam CI tata
                if (model.CopieCIT.Length > 0)
                {
                    string fileNameCIT = Path.GetFileName(model.CopieCIT.FileName);
                    Attachment file2 = new Attachment(model.CopieCN.OpenReadStream(), fileNameCIT, MediaTypeNames.Application.Octet);
                    mm.Attachments.Add(file2);
                    //fie2.Dispose();
                    //mm.Attachments.Add(new Attachment(model.CopieCN.OpenReadStream(), fileNameCIT, MediaTypeNames.Application.Octet));
                }
                //atasam CI mama
                if (model.CopieCIM.Length > 0)
                {
                    string fileNameCIM = Path.GetFileName(model.CopieCIM.FileName);
                    Attachment file3 = new Attachment(model.CopieCN.OpenReadStream(), fileNameCIM, MediaTypeNames.Application.Octet);
                    mm.Attachments.Add(file3);
                    //file3.Dispose();
                    //mm.Attachments.Add(new Attachment(model.CopieCN.OpenReadStream(), fileNameCIM, MediaTypeNames.Application.Octet));
                }

                //here we try another approach for multi attach
                //first we create a list of files
                List<string> AttachList = new List<string>();
                AttachList.Clear();
                if (model.CopieCN.Length > 0)
                {
                    AttachList.Add(Path.GetFileName(model.CopieCN.FileName));
                }
                if (model.CopieCIT.Length > 0)
                {
                    AttachList.Add(Path.GetFileName(model.CopieCIT.FileName));
                }
                if (model.CopieCIM.Length > 0)
                {
                    AttachList.Add(Path.GetFileName(model.CopieCIM.FileName));
                }
                //

                foreach (var filepath in AttachList) //this is commented in real life
                {
                    var attachment = new Attachment(filepath);   // here you can attach a file as a mail attachment  
                    mm.Attachments.Add(attachment);
                }
                //

                using (SmtpClient smtp = new SmtpClient())
                {
                    smtp.Host = "smtp.gmail.com";
                    smtp.EnableSsl = true;
                    NetworkCredential NetworkCred = new NetworkCredential("sender.email@gmail.com", "@Password@");
                    smtp.UseDefaultCredentials = true;
                    smtp.Credentials = NetworkCred;
                    smtp.Port = 587;

                    try {
                        smtp.Send(mm);
                    ViewBag.Message = "Mesaj trimis cu succes."; }
                    catch (Exception ex) {
                        ViewBag.Message = ("S-a produs o eroare: {0}", ex.ToString());
                    }
                    finally
                    {
                        //Clear all the form's fields
                    }


            }
            }

            return View();
            //return new RedirectResult("https://www.some-site.com");
        }

Here comes the error:

/*Error rised*/

/*line 105 is: smtp.Send(mm); */

(S-a produs o eroare: {0}, System.Net.Mail.SmtpException: Failure sending mail. ---> System.InvalidOperationException: The inner stream position has changed unexpectedly. at Microsoft.AspNetCore.Http.ReferenceReadStream.VerifyPosition() at Microsoft.AspNetCore.Http.ReferenceReadStream.Read(Byte[] buffer, Int32 offset, Int32 count) at System.Net.Mime.MimePart.Send(BaseWriter writer, Boolean allowUnicode) at System.Net.Mime.MimeMultiPart.Send(BaseWriter writer, Boolean allowUnicode) at System.Net.Mail.Message.Send(BaseWriter writer, Boolean sendEnvelope, Boolean allowUnicode) at System.Net.Mail.SmtpClient.Send(MailMessage message) --- End of inner exception stack trace --- at System.Net.Mail.SmtpClient.Send(MailMessage message) at Inscrieri.Inima.Controllers.HomeController.Index(EmailModel model) in C:\Users\laurentiu\source\repos\Inscrieri.Inima\Inscrieri.Inima\Controllers\HomeController.cs:line 105)

Any hint will be appreciated.

Regards