SMTP Server Authentication Error: How Can I Troubleshoot and Resolve '5.5.1 Authentication Required'?

SMTP Server Authentication Error: Troubleshooting and Resolution

This article will provide a comprehensive solution to the common SMTP server authentication error "5.5.1 Authentication Required".

This error message indicates that the SMTP server requires a secure connection or client authentication. This means that you need to establish a secure connection and provide valid credentials to authenticate to the SMTP server before you can send an email.

To resolve this error, please follow these steps:

1. Enable low-security apps in your Google Account:

   • Sign in to your Google Account and visit https://www.php.cn/link/0a8a64171a9145f6a47e5b3544632e3b or https://www.php.cn/link/96a83c96abbe6d0b40c72b279ebdf76e.
   • Enable the "Low-security apps" feature to allow access from low-security apps, including SMTP clients.

2. Configure SMTP credentials:

   • In your code, you need to specify the correct SMTP server, port, and credentials. Make sure you are using the correct username and password for your email account.
   • You can use the following code snippet:

using (MailMessage mail = new MailMessage())
{
    mail.From = new MailAddress("[email protected]");
    mail.To.Add("[email protected]");
    mail.Subject = "Hello World";
    mail.Body = "<h1>Hello</h1>";
    mail.IsBodyHtml = true;

    using (SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587))
    {
        smtp.Credentials = new NetworkCredential("[email protected]", "password");
        smtp.EnableSsl = true;
        smtp.Send(mail);
    }
}

3. Verify connection settings:

   • Make sure your code uses the correct SMTP server settings. For Gmail, use "smtp.gmail.com" and port 587.
   • Make sure your code uses TLS encryption by setting EnableSsl to true.

4. Disable firewall or anti-virus software:

   • In some cases, firewalls or antivirus software may block outbound connections to SMTP servers. Temporarily disable these applications to test whether they are blocking email delivery.

5. Check Web.config settings:

   • In your Web.config file, verify that the SMTP credentials, server settings, and enableSsl values ​​are correct.

Follow these steps and you should be able to resolve SMTP server authentication errors and successfully send emails.

The above is the detailed content of SMTP Server Authentication Error: How Can I Troubleshoot and Resolve '5.5.1 Authentication Required'?. For more information, please follow other related articles on the PHP Chinese website!