title: SMTP error could not Authenticated using SMTP in .Net core
body: <p>Credentials were Correct.
  5.7.57 SMTP - Client was not authenticated to send mail, 535 5.7.139 Authentication unsuccessful</p>
  <p>returning this error while sending email using SMTP in .Net</p>
  <p>This Application is deployed in Azure
  Not sure what is causing the issue, previoulsy it was working suddenly it stopped.</p>
  <p>Tried with Exchange Server throwing 401 unAuthorized error.</p>