Send Email Using C# the Smtp Server Requires a Secure Connection or the Client Was Not Authenticated [Duplicate]

Name: Send Email Using C# the Smtp Server Requires a Secure Connection or the Client Was Not Authenticated [Duplicate]
Uploaded: 2026-09-29T14:33:33+00:00
Duration: 22 min 34 s
Description: I Was Create Sample Email Sender Using C# but It Shows an Error Is: the Smtp Server Requires a Secure Connection or the Client Was Not Authenticated. the...

Question

I was create sample email sender using c# but it shows an error is:

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

private void SendHtmlFormattedEmail(string recepientEmail, string subject, string body)
{
    using (MailMessage mailMessage = new MailMessage())
    {
       mailMessage.From = new MailAddress("[email protected]");
       mailMessage.Subject = subject;
       mailMessage.Body = body;
       mailMessage.To.Add(new MailAddress(recepientEmail));
       SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587);
       smtp.EnableSsl = true;
       smtp.UseDefaultCredentials = false;
       System.Net.NetworkCredential NetworkCred = new System.Net.NetworkCredential("[email protected]", "XXXXXXXXX");
       smtp.Credentials = NetworkCred;
       smtp.Timeout = 10000;
       smtp.Send(mailMessage);
    }
}

please help me for sample mail sender code

Status:System.Net.Mail.SmtpStatusCode.MustIssueStartTlsFirst

Accepted Answer

Try swapping these lines like so:

smtp.UseDefaultCredentials = false;
System.Net.NetworkCredential NetworkCred = new    System.Net.NetworkCredential("[email protected]", "XXXXXXXXX");

Answer 2

I went to the following link:

and turned on the option Access for less secure apps

Send Email Using C# the Smtp Server Requires a Secure Connection or the Client Was Not Authenticated [Duplicate]

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2 Answers

Robert Thorne