Why Am I Getting an 'SMTP Server Requires Authentication' Error When Sending Emails from My Application?

Troubleshooting SMTP Server Authentication Errors in Google Accounts

Issue:

Sending emails via SMTP from a local application results in the error: "The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required." Even with SSL enabled and correct credentials, the problem persists.

Resolution:

This error usually signifies that your Google account's "less secure app access" setting is disabled. Here's how to fix it:

1. Access your Google account.
2. Go to Account > Security > Less secure app access.
3. Enable the Less secure app access option.

Code Example (C#):

The following C# code demonstrates how to send an email after enabling less secure app access:

<code class="language-csharp">using System.Net.Mail;
using System.Net;

MailMessage mail = new MailMessage();

mail.From = new MailAddress("your_email@gmail.com"); // Replace with your email
mail.To.Add("recipient_email@example.com"); // Replace with recipient's email
mail.Subject = "Test Email";
mail.Body = "Test Email Content";
mail.Priority = MailPriority.High;

SmtpClient client = new SmtpClient();

client.Credentials = new NetworkCredential("your_email@gmail.com", "your_password"); // Replace with your credentials
client.Host = "smtp.gmail.com";
client.Port = 587;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.EnableSsl = true;
client.UseDefaultCredentials = false;

client.Send(mail);</code>

Important Considerations:

• While enabling less secure app access allows older applications to connect, it's less secure than alternatives like OAuth 2.0. Consider migrating to OAuth 2.0 for enhanced security.
• Google may disable less secure app access in the future, so a more secure authentication method is recommended for long-term stability.

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