The SMTP server requires a secure connection or the client was not authenticated

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The SMTP server requires a secure connection or the client was not authenticated

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#1 by (7 votes)
#2 by (0 votes)

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I'm having the following error when working with SMTP and MailMessage in C #:

The SMTP server requires a secure connection or the client was not authenticated. The response from the server was: 5.5.1 Requested Authentication Learn more at

Or in English

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at

    /// <summary>
    /// Servidor de E-mail
    /// </summary>
    protected SmtpClient SmtpClient { get; set; }

    /// <summary>
    /// Conteudo da Mensagem
    /// </summary>
    protected MailMessage MailMessage { get; set; }
    #endregion 

   /// <summary>
   /// Método enviar e-mail
   /// </summary>
   /// <param name="smtp"></param>
   /// <param name="from"></param>
   /// <param name="to"></param>
   /// <param name="subject"></param>
   /// <param name="body"></param>
   /// <param name="priority"></param>
    public string EnviarEmail(string smtp, string from, string to, string subject, string body, bool priority)
    {
        try
        {
            SmtpClient = new SmtpClient();
            SmtpClient.Host = "smtp.gmail.com";
            SmtpClient.Port = 587;
            SmtpClient.EnableSsl = true;
            SmtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;
            SmtpClient.Credentials = new NetworkCredential("[email protected]","senha");
            SmtpClient.UseDefaultCredentials = true;

            MailMessage = new MailMessage();
            MailMessage.From = new MailAddress(from, "Raffa Ferreira", Encoding.UTF8);
            MailMessage.To.Add(new MailAddress(to, "Fulano teste", Encoding.UTF8));

            MailMessage.Subject = subject;
            MailMessage.Body = body;
            MailMessage.BodyEncoding = Encoding.UTF8;
            MailMessage.BodyEncoding = Encoding.GetEncoding("ISO-8859-1");

            if (priority == false)
            {
                MailMessage.Priority = MailPriority.Normal;
            }
            else
            {
                MailMessage.Priority = MailPriority.High;
            }

            SmtpClient.Send(MailMessage);
        }
        catch(SmtpFailedRecipientException ex)
        {
            Console.WriteLine("Mensagem : {0} " + ex.Message);
        }
        catch(SmtpException ex)
        {
            Console.WriteLine("Mensagem SMPT Fail : {0} " + ex.Message);
        }
        catch(Exception ex)
        {
            Console.WriteLine("Mensagem Exception : {0} " + ex.Message);
        }

        string mensagem = "E-mail enviado";
        return mensagem;
    }

What I'm doing wrong, I understood the error message. I've tried changing e-mail and senha , this is my first time using SMTP . I know it's not difficult, just a lack of attention from me.

I've been looking for some helps elsewhere, but I did not find anything to help me, I hope you can help me.

c# smtp

asked by anonymous 03.10.2015 / 02:06

2 answers

0

If you prefer not to allow access to less secure applications, the following solution can be adopted:

Log in to the gmail account that will be used by the site select "My Account"
Select the "Login and security" option
Enable "2-step verification" (follow the requested procedures)
Select the "App Passwords" option (follow the requested procedures)
Select the "Select app" option
Choose the "Other (custom name)" option
Enter the name of your site / webapp
Copy the password generated by google
In the code snippet below, enter the generated password instead of the account password:

SmtpClient.Credentials = new NetworkCredential ("[email protected]", "password generated by google");

This is done, your webapp or website will be able to connect to the account without being blocked by google security and without reducing the level of security.

11.01.2017 / 01:04

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score 7 · Accepted Answer

To use Gmail, UseDefaultCredentials must be false . This property must be set before credentials, like this:

SmtpClient.UseDefaultCredentials = false;
SmtpClient.Credentials = new NetworkCredential("[email protected]","senha");

You should also allow "less secure" access to your Gmail through the Less secure apps page.