System.net.mail.smtpstatuscode.mustissuestarttlsfirst

A specific error!

System.Net.Mail.SmtpStatusCode.MustIssueStartTlsFirst is an error code returned by the SMTP server when it requires the client to issue a STARTTLS command before sending any other commands.

Here's what's happening:

  1. Your application is trying to send an email using the System.Net.Mail namespace.
  2. The SMTP server (e.g., Gmail, Outlook, etc.) requires the client to use TLS (Transport Layer Security) encryption to send emails.
  3. The SMTP server is responding with a MustIssueStartTlsFirst error code, indicating that the client must issue a STARTTLS command before sending any other commands.

To resolve this issue, you need to modify your code to issue a STARTTLS command before sending the email. Here's an example in C#:

using System.Net.Mail;
using System.Net.Security;

// Create an SMTP client
SmtpClient client = new SmtpClient();

// Set the SMTP server and port
client.Host = "smtp.gmail.com";
client.Port = 587;

// Set the encryption method
client.EnableSsl = true;

// Set the username and password
client.Credentials = new NetworkCredential("[email protected]", "your_password");

// Create a mail message
MailMessage message = new MailMessage("[email protected]", "[email protected]", "Subject", "Body");

// Issue the STARTTLS command
client.GetResponse();

// Send the email
client.Send(message);

In this example, we set EnableSsl to true to enable TLS encryption. Then, we issue the STARTTLS command using GetResponse() before sending the email.

If you're using a different SMTP client library or framework, you may need to consult its documentation for specific instructions on how to issue the STARTTLS command.