خطا هنگام ارسال ایمیل فعال سازی

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این خطا میده 

System.Net.Mail.SmtpException
  HResult=0x80131500
  Message=The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at
  Source=System.Net.Mail
  StackTrace:
   at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response)
   at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode)
   at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)
   at System.Net.Mail.SmtpClient.Send(MailMessage message)
   at Amlakyar.Core.Senders.SendEmail.Send(String to, String subject, String body) in E:\h\Webamlakyar\amlakyar.Core\Senders\SendEmail.cs:line 29
   at WebAmlakyar.Controllers.AccountController.Register(RegisterViewModel register) in E:\h\Webamlakyar\Webamlakyar\Controllers\AccountController.cs:line 76
   at Microsoft.Extensions.Internal.ObjectMethodExecutor.Execute(Object target, Object[] parameters)
   at Microsoft.AspNetCore.Mvc.Internal.ActionMethodExecutor.SyncActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeActionMethodAsync>d__12.MoveNext()

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