Send email form Gmail account using C#

Question

When sending an email using the followng code, I'm getting an error, I'm asking for your help.

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string adSoyad = txtAdSoyad.Text;
string konu = "Koçaslanlar Web Konu başlığı";
string epostaAdresi = txtMail.Text;
string mesaji = txtMessage.Text;
string ipAdresi = ":44372"; //gönderenin IP adresini alıyoruz (localde 127.0.0.1 yada ::1 şeklinde gözükür)
if (HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"] != null)
    ipAdresi = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"].ToString();
else if (HttpContext.Current.Request.UserHostAddress.Length != 0)
    ipAdresi = HttpContext.Current.Request.UserHostAddress;

string mesajIcerik = "";
mesajIcerik += "<b>İletişim Formundan Gelen Mesaj</b> / " + DateTime.Now.ToString() + " / " + ipAdresi + "<br/>";
mesajIcerik += "<b>Adı Soyadı: </b>" + adSoyad + "<br/>";
mesajIcerik += "<b>E-posta: </b>" + epostaAdresi + "<br/>";
mesajIcerik += "<b>Konu: </b>" + konu + "<br/>";
mesajIcerik += "<b>İleti: </b>" + mesaji;

MailMessage yeniMesaj = new MailMessage();
yeniMesaj.IsBodyHtml = true;
yeniMesaj.To.Add(epostaAdresi);//buraya alıcı mail adresiniz gelecek
yeniMesaj.From = new MailAddress("******@gmail.com", "KOÇASLANLAR HOLDİNG", System.Text.Encoding.UTF8);
yeniMesaj.Subject = "Yeni Mesaj: " + adSoyad + " - " + konu;
yeniMesaj.Body = mesajIcerik;

SmtpClient gonder = new SmtpClient();

gonder.Credentials = new System.Net.NetworkCredential("******@gmail.com", "password");
gonder.Port = 587;
gonder.Host = "smtp.gmail.com";
gonder.EnableSsl = true;
gonder.UseDefaultCredentials = false;
gonder.Send(yeniMesaj);
lblMessage.Text = "send message!";
lblMessage.ForeColor = System.Drawing.ColorTranslator.FromHtml("#00a186");

Answer 1

Looking into the code, it looks like you want to send email from Gmail. So you first need to do the following steps:

1. Go to https://myaccount.google.com/security
2. Enable 2-Step Verification
3. Click on App passwords and add a new App, let's say "MySampleApp" and generate a password for it. Copy the password (it's 16 characters without any space).
4. Then you can use this password from sending email on behalf of yourself.

Now you can use the following code to send email:

using (var client = new SmtpClient())
{
    client.Host = "smtp.gmail.com";
    client.Port = 587;
    client.DeliveryMethod = SmtpDeliveryMethod.Network;
    client.UseDefaultCredentials = false;
    client.EnableSsl = true;
    client.Credentials = new NetworkCredential("******@GMAIL.COM", "APP_PASSWORD");
    using (var message = new MailMessage(
        from: new MailAddress("******@GMAIL.COM", "YOUR NAME"),
        to: new MailAddress("******@ANYWHERE.COM", "THEIR NAME")
        ))
    {

        message.Subject = "Hello from code!";
        message.Body = "Loremn ipsum dolor sit amet ...";

        client.Send(message);
    }
}