How solve SMTP error for send mail

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hi. I try create asp.net core MVC with .NET 7. I create class for send email to user for confirm their email. but I get this error:

SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required. Learn more at
System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, string response)

how can I fix this?

What I have tried:

MynMessageSender class is:

public class MessageSender : IMessageSender
   {

       private readonly IConfiguration _configuration;
       public MessageSender(IConfiguration configuration)
       {
           _configuration = configuration;
       }
       public Task SendEmailAsync(string toEmail, string subject, string message, bool isMessagehtml = false)
       {

           using (var client = new SmtpClient())
           {
               var credentails = new NetworkCredential()
               {
                   UserName = _configuration.GetValue<string>("websiteGmail:Mail"), // withiout @gmail.com
                   Password = _configuration.GetValue<string>("websiteGmail:Password")
               };
               client.Credentials = credentails;
               client.Host = "smtp.gmail.com";
               client.Port = 587;
               client.EnableSsl = true;

               using var emailMesage = new MailMessage()
               {
                   To = { new MailAddress(toEmail) },
                   From = new MailAddress(_configuration.GetValue<string>("websiteGmail:FullEmailAddress")!),
                   Subject = subject,
                   Body = message,
                   IsBodyHtml = isMessagehtml
               };
               client.Send(emailMesage);
           }
           return Task.CompletedTask;
       }
   }

and in register action after user create account successfully my code is:

await userManager.AddToRoleAsync(user, "User");

                   var emailConfirmationToken = await userManager.GenerateEmailConfirmationTokenAsync(user);
                   var emailMessage =
                       Url.Action("ConfrimEmail", "Sign", new {username = user.UserName,token = emailConfirmationToken},
                       Request.Scheme);

                   await _messageSender.SendEmailAsync(user.Email, "Email Confirmation" , emailMessage);

Posted 24-Sep-23 2:50am

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Graeme_Grant · Accepted Answer · 2023-09-24T12:43:00

With GMail, you don't use your normal account and password. You need to generate a "special" app paasword for the email address that you want to use. Please read this: Sign in with app passwords - Gmail Help[^]

Here is a quick'n'dirty (tested & working) .Net 7.0 console app to test with:

C#

using System.Diagnostics;
using System.Net.Mail;
using System.Net;

var smtpClient = new SmtpClient("smtp.gmail.com")
{
    Port = 587,
    Credentials = new NetworkCredential(
        "[gmail email address]",
        "[generated app password]"),
    EnableSsl = true,
};

try
{
	smtpClient.Send(
        from: "[gmail email address]",
        recipients: "[one or more recipient email addresses]",
        subject: "Test message",
        body: "This is a test message sent from .Net 7.0 application");

}
catch (SmtpException ex)
{

	Debugger.Break();
}