c# ASP.Net Mail-Error "无法连接到远程服务器"

Question

private void MailGonder(string to, string from, string password, string subject, string body, HttpPostedFile ektekidosya)
{
    using (MailMessage mm = new MailMessage(from, to))
    {
        mm.Subject = subject;

        mm.Body = body;

        mm.IsBodyHtml = false;

        SmtpClient smtp = new SmtpClient();

        smtp.Host = "smtp.gmail.com";

        smtp.EnableSsl = true;

        NetworkCredential NetworkCred = new NetworkCredential(from, password);

        smtp.UseDefaultCredentials = false;

        smtp.Credentials = NetworkCred;

        smtp.Port = 587;

        smtp.Send(mm);
    }
}
    protected void BtnGonder_Click(object sender, EventArgs e)
    {
        string to = txtKime.Text;

        string from = txtEmail.Text;

        string password = txtPassword.Text;

        string subject = txtKonu.Text;

        string body = txtMesaj.Text;

        HttpPostedFile ektekidosya = fuAttach.PostedFile;

        try
        {
            MailGonder(to, from, password, subject, body, ektekidosya);
            Response.Write("Mail başarıyla gönderildi");
        }
        catch (Exception ex)
        {
            Response.Write("Mail gönderiminde hata oluştu. Err: " + ex.ToString());
        }
    }

我尝试了不同的端口，但没有任何帮助，我不断收到错误消息。Localserver 工作正常，但 Server 没有工作。我该如何解决这个错误？ 我什么都试过了。我的主机是 1und1。

Here Picture from my Website Error

Answer 1

尝试将“smtp.UseDefaultCredentials = true;”表达式BEFORE放在NetworkCredential声明中：

smtp.UseDefaultCredentials = false;
NetworkCredential NetworkCred = new NetworkCredential(from, password);

顺序很重要，因为设置 SmtpClient.UseDefaultCredentials = false 会将 SmtpClient.Credentials 重置为 null。

更新：

1) 先用 telnet 检查：

Telnet smtp.gmail.com 587 如果您看到一个空的命令提示符窗口，则说明连接成功

2) 确保发件人地址与您传递的凭据关联的 gmail 帐户相同

3) 如果您的密码很弱，gmail 可能无法发送您的邮件！

4) 如果这不起作用，请使用另一个邮件服务器

Answer 2

使用 gmail 确保允许不太安全的应用访问

Check here Let less secure apps use your account