Why Is My C# Gmail SMTP Email Sending Failing, and How Can I Fix It?

Debugging C# Gmail SMTP Email Sending Problems

Many developers using the popular Stack Overflow guide "Sending email in .NET through Gmail" still encounter email delivery issues. This article explores common causes and offers alternative solutions.

A frequent error is "5.5.1 Authentication Required." This indicates authentication failure with the Gmail SMTP server. Verify your Gmail credentials and the authentication section of your C# code.

Gmail's security settings are another potential culprit. Gmail requires enabling "less secure apps" access for enhanced security. Check your Gmail security settings to ensure this is activated. Note that this is generally discouraged for security reasons; see below for a more secure approach.

If these steps don't resolve the problem, review your C# code thoroughly. Confirm that your SMTP settings (server address, port, and SSL usage) are accurate.

For a robust solution, consider this improved C# code example: (Note: Replace bracketed placeholders with your actual email and password.)

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

public class EmailSender
{
    public static void SendEmail(string fromAddress, string password, string toAddress, string subject, string body)
    {
        using (var client = new SmtpClient("smtp.gmail.com", 587))
        {
            client.EnableSsl = true;
            client.Credentials = new NetworkCredential(fromAddress, password);
            var message = new MailMessage(fromAddress, toAddress, subject, body);
            client.Send(message);
            Console.WriteLine("Email sent successfully!");
        }
    }

    public static void Main(string[] args)
    {
        string fromEmail = "[email protected]";
        string password = "mypwd"; // Consider using a more secure method like an App Password
        string toEmail = "[email protected]";
        string subject = "Test Email";
        string body = "Test email body";

        SendEmail(fromEmail, password, toEmail, subject, body);
        Console.ReadKey();
    }
}</code>

Important Security Note: Using "less secure apps" is strongly discouraged. For a more secure approach, generate an App Password in your Gmail account settings and use that instead of your regular password in the C# code. This provides a dedicated password for your application without compromising your main Gmail account security. Refer to Google's documentation for instructions on generating App Passwords.

By implementing these suggestions and carefully checking your code, you should successfully send emails via Gmail's SMTP server using C#.

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