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

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I’m having the following mistake, working with SMTP and MailMessage in the C#:

The SMTP server requires a secure connection or the client has not been authenticated. The server response was: 5.5.1 Requested authentication Learn more on

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 got the message of the mistake. I tried to change the e-mail and the senha, is the first time I’ve used SMTP I’m new at this. I know it’s not hard, just a lack of attention from me.

For now I’ve looked for some helps in other places, but I couldn’t find anything to help me, I hope you can help me.

c# emailing smtp

  • You can do log in on Gmail on the same machine where you’re running this? I hope you haven’t posted your password for everyone to see.

  • I didn’t post no, where is "password" is something fictitious. I just logged in with the same email and password, and logged in normally. But during the execution of the project, he brings me this failure.

  • When you loga on Gmail, does it ask for access confirmation? Does it indicate unusual usage? See this? https://security.google.com/settings/security/activity Have you tried to change this? https://www.google.com/settings/security/lesssecureapps

  • It shows me some access quests, Devices and PC’s !

2 answers

9


To use Gmail, UseDefaultCredentials must be false. This property must be defined before of credentials, thus:

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

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

  • Okay, thank you very much !

  • @Raffaferreira or make your application use XOAUTH, so you don’t need to authorize less secure applications.

  • "Less secure apps.".. That’s what was wrong with me.rs

  • After a lot of running the Internet, finally that was the cause. It really helped a lot!

  • I had the same problem and the solution was in gmail itself in authorizing applications. Thank you very much.

0

If you prefer not to allow access from 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 "Login and security"
  • Activate "Two-Step Verification" (follow the requested procedures)
  • Select the "App passwords" option (follow the requested procedures)
  • Select the option "Select app"
  • Choose "Other (custom name)"
  • Enter the name of your website / webapp
  • Copy the google generated password

  • 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 done, your webapp or website will be able to connect to the account without being barred by google security and without reducing the security level.

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